Intellectual Disability: What It Means and What Support Looks Like

What does intellectual disability mean?

Intellectual disability refers to neurodevelopmental conditions that affect functioning in two areas: cognitive functioning, such as learning, problem solving and judgment, and adaptive functioning, the activities of daily life such as communication and social participation.⁠³ It is a developmental disability, and each person with it has their own strengths and weaknesses.⁠⁴ It is lifelong, but early and ongoing intervention may improve functioning.⁠³

The core of the definition has been stable for decades. The AAIDD, the American Psychiatric Association and the World Health Organization have agreed for more than 50 years on its three essential elements: substantial limitations in intellectual functioning, substantial limitations in adaptive behavior, and onset during the developmental period.⁠⁵

What is the DSM-5-TR definition of intellectual disability?

The DSM-5 named the condition intellectual disability (intellectual developmental disorder), replacing the term used in earlier editions, and the DSM-5-TR (2022) uses the same term.⁠^1,3 Its criteria require deficits in intellectual functions, such as reasoning, problem solving, planning, abstract thinking, judgment, academic learning and learning from experience; deficits in adaptive functioning, meaning a failure to meet developmental and sociocultural standards for personal independence and social responsibility; and onset during the developmental period.⁠^1,6 The deficits are established by both clinical assessment and standardized testing, not by a test score alone.⁠^1,6

How does the AAIDD define intellectual disability?

The American Association on Intellectual and Developmental Disabilities defines it as a condition characterized by significant limitations in both intellectual functioning and adaptive behavior that originates before the age of 22.⁠² Its 12th edition manual, published in 2021, sets both thresholds at about 2 or more standard deviations below the mean: on a standardized intelligence test, and on a standardized adaptive behavior test in one or more of the conceptual, social and practical domains.⁠⁴ Clinical judgment plays a role in every part of the determination.⁠⁴

What are the three defining criteria for intellectual disability?

All three must be met: limitations in intellectual functioning, limitations in adaptive behavior, and onset during the developmental period.⁠^2,5

What counts as a significant limitation in intellectual functioning?

Intellectual functioning, also called intelligence, means general mental capacity, such as learning, reasoning and problem solving.⁠² The usual measure is an IQ test, and a score of around 70, or as high as 75, indicates a significant limitation.⁠² The APA notes that 68% of people score between 85 and 115, that subtest scores can vary considerably, and that a full-scale score may not reflect overall functioning, so clinical judgment is needed to interpret it.⁠³

What is adaptive behavior, and what are its three domains?

Adaptive behavior is the collection of conceptual, social and practical skills that people learn in order to function in daily life. It is a different concept from intelligence: these are learned behaviors that reflect a person’s social and practical competence.⁠¹⁵

• Conceptual. Language, reading, writing, math, reasoning, knowledge and memory.⁠³
• Social. Empathy, social judgment, communication skills, following rules, and making and keeping friendships.⁠³
• Practical. Independence in personal care, job responsibilities, managing money, recreation, and organizing school and work tasks.⁠³

The skills a person needs change as the world does: the AAIDD’s example is that making a phone or video call today takes different skills from those required 20 years ago.⁠¹⁵

Is a limitation in physical functioning one of the criteria?

No. The three criteria are intellectual functioning, adaptive behavior and onset during the developmental period; physical functioning is not among them.⁠^2,5 Conditions that affect the body, such as cerebral palsy and epilepsy, often occur alongside intellectual disability, but they are separate diagnoses.⁠³

At what age must intellectual disability begin?

During the developmental period, which the AAIDD defines as before age 22: both limitations must have appeared before the person turns 22.⁠^2,4 The DSM-5 sets no specific age requirement, only that symptoms begin during the developmental period.⁠¹ Some sources still use 18: the APA’s patient guide says the deficits typically begin before age 18 for diagnosis, and NICHD says intellectual disability starts any time before a child turns 18.⁠^3,16

Why did the AAIDD change the developmental period from 18 to 22?

The 12th edition moved the end of the developmental period from before age 18 to before age 22 on the basis of research showing that important brain development continues into the 20s. The AAIDD adds that age 22 is consistent with the standards used for diagnosis in the DSM-5 and ICD-11 and with service eligibility at the US Social Security Administration.⁠⁴

The change is not expected to raise prevalence, because the vast majority of diagnoses are made in early childhood; it allows an accurate diagnosis for the small percentage of people identified nearer the end of the developmental period.⁠⁴

When is intellectual disability usually recognized?

The more severe the limitations, the earlier. Profound intellectual disability is usually recognized by age 2, severe by age 3 or earlier, and moderate by 3 to 5 years; mild intellectual disability is less likely to be recognized before 5 to 6 years of age.⁠⁶ Standardized tests are hard to use in very young children, so the term global developmental delay is usually kept for children younger than 5, and intellectual disability for older children for whom IQ testing is valid and reliable.⁠^6,9 More on global developmental delay.

Does an IQ score diagnose intellectual disability or set severity?

Neither, on its own. The DSM-5 removed IQ scores from the diagnostic criteria while keeping them in the text description, so that they are not overemphasized as the defining factor of a person’s overall ability without adequate consideration of functioning; the APA called this especially important in forensic cases.⁠¹

IQ testing still belongs in the assessment. The DSM-5 places intellectual disability at about two standard deviations or more below the population mean, an IQ of about 70 or below, and the APA’s patient guide says a specific full-scale IQ score is no longer required for diagnosis, though standardized testing is still used.⁠^1,3 Measured IQ may or may not correlate with adaptive functioning, so IQ alone is not considered sufficient to decide whether a person has an intellectual disability or how severe it is.⁠⁶

What are the four severity levels of intellectual disability?

Mild, moderate, severe and profound. In the DSM-5 the levels rest on adaptive functioning rather than IQ scores alone, and the level of adaptive functioning and the intensity of support needed are the main criteria for placing a person in one.⁠^1,6 Most people with an intellectual disability are in the mild range.⁠³

Severe and profound intellectual disability are told apart mainly by differences in adaptive behavior, because standardized intelligence tests are not clearly valid at the lowest scores.⁠⁶

How do the AAIDD support levels compare with the DSM severity levels?

The AAIDD describes the level of intellectual disability by the supports a person needs to function in daily life: intermittent, limited, extensive or pervasive. The DSM-5 uses mild, moderate, severe and profound.⁠¹⁸ Both point toward support, and the AAIDD says the overarching reason to evaluate and classify is to tailor a personalized set of supports.⁠^4,18

What causes intellectual disability?

Many things. The AAIDD groups the causes by risk factor, biomedical, social, behavioral and educational, and by when exposure happens: before birth, around birth or after birth.⁠⁴ A specific cause is found in more than 75% of people with severe intellectual disability but less often in mild intellectual disability, where environmental and psychosocial factors such as low maternal education, malnutrition and poor access to health care weigh more.⁠⁶

Can causes of intellectual disability be prevented or treated early?

Some. Fetal alcohol spectrum disorders are preventable if a developing baby is not exposed to alcohol.⁠²¹ Every US state screens newborns for many serious conditions using a few drops of blood from the baby’s heel.⁠²³ Untreated phenylketonuria lets phenylalanine build up to harmful levels and causes intellectual disability, which is why early identification of treatable inborn errors of metabolism matters.⁠^6,22 Better prenatal care, newborn screening and immunization all contribute to lower rates of intellectual disability.⁠⁶

How is intellectual disability diagnosed and assessed?

Through a comprehensive evaluation rather than a single test. Intellectual functioning is measured with individually administered, culturally appropriate intelligence tests, and adaptive functioning with standardized measures and interviews with family members, teachers and caregivers.⁠³ A diagnosis also draws on the clinical history, physical and neurological examination, and clinical judgment.⁠^4,6 Hearing and vision should be checked in every child being evaluated.⁠⁶

Who can diagnose intellectual disability?

Specialists such as developmental pediatricians, child neurologists, and child psychologists or psychiatrists, often after a referral from the child’s doctor.⁠²⁴ A speech-language pathologist does not make the diagnosis, though the SLP’s findings can help the professionals who do.⁠¹⁸ Schools evaluate separately for special education, and a parent can ask for that evaluation without waiting for a medical diagnosis.⁠^24,25

What tests are used to assess intellectual disability?

Two kinds of standardized test, alongside history and observation. For intelligence, an individually administered IQ test; for adaptive behavior, a standardized scale such as the Vineland Adaptive Behavior Scales, on which diagnosis calls for a score about two standard deviations below the norm.⁠³ The AAIDD publishes its own Diagnostic Adaptive Behavior Scale.⁠² Every result has to be read with possible sources of testing error in mind.⁠⁴

Can a test be unfair to a child’s language or culture?

It can, which is why the rules guard against it. School evaluations under IDEA must not discriminate on a racial or cultural basis, must be given in the child’s native language or usual mode of communication, and must include tools for specific areas of need, not only a single general intelligence quotient.⁠²⁶ The AAIDD asks professionals to consider linguistic diversity and cultural differences in the way people communicate, move and behave.⁠² Testing should also allow for a child’s motor, behavioral and language differences.⁠⁶ If your child is still learning English, raise it before testing begins.⁠²⁶

Should a child with intellectual disability have genetic testing?

Often, when the cause is not known. The American Academy of Pediatrics designates chromosomal microarray as a first-line test for a child with intellectual disability of unknown cause, and fragile X testing remains an important first-line test.⁠⁹ The American College of Medical Genetics and Genomics strongly recommends that exome or genome sequencing be considered as a first- or second-tier test, citing a higher diagnostic yield than standard testing.⁠¹⁰

Finding a cause can help anticipate complications, identify a treatable condition, plan services, provide genetic counseling for the family and open access to research and support services.⁠⁶ The CDC notes that a fragile X diagnosis can help a family by giving a reason for a child’s intellectual disability and behavior.⁠²⁰

What conditions often occur alongside intellectual disability?

Autism, cerebral palsy, epilepsy, ADHD, impulse control disorder, depression and anxiety frequently co-occur.⁠³ Mental health conditions are especially common: about 40% of children with an intellectual disability have a diagnosable mental disorder, at least double the rate in other children.⁠¹¹ An earlier systematic review put the rate at 30 to 50%.⁠²⁷ Related guides: Autism, ADHD, epilepsy and cerebral palsy.

How many children have an intellectual disability?

About 1% of the population has an intellectual disability, according to the APA, which adds that 2 to 3% of children in high-income countries do.⁠³ A meta-analysis of 52 population studies put the overall prevalence at 10.37 per 1,000, with higher rates in low- and middle-income countries and in studies of children.⁠²⁹

In the United States, the National Health Interview Survey found that 1.65% to 2.20% of children aged 3 to 17 had ever been diagnosed with an intellectual disability during 2019 to 2021, with no significant change across those years. Diagnosis was more common in boys (2.31%) than in girls (1.37%), and rose with age, from 1.39% at 3 to 7 years to 2.35% at 13 to 17.⁠⁷

What language should you use about intellectual disability?

Person-first language is the long-standing convention: “a child with an intellectual disability,” “people with intellectual disabilities.” The move to person-first terms in the early 1980s reflected the idea that the disability does not define the person.⁠^18,30 Terminology continues to evolve, and some people prefer identity-first language; ASHA follows the APA style manual, which says to use the terms the individual prefers.⁠^18,30

APA style also advises against negative labels, terms that imply restriction, and slurs.⁠³⁰ Describing a child by an IQ score or a severity level, as though it were who they are, runs against the same principle that puts the person before the condition.⁠³⁰

What is Rosa’s Law?

Rosa’s Law, Public Law 111-256, was enacted on October 5, 2010. It changed references in federal law from “mental retardation” to “intellectual disability,” including in the Individuals with Disabilities Education Act.⁠¹⁴ IDEA’s definition itself did not change, only the name.⁠³¹ The DSM-5, published in 2013, made the same change in psychiatric diagnosis.⁠¹ The AAIDD notes that older documents using the former term should be read in their historical or legal context.⁠⁵

Is intellectual disability a disability category under IDEA?

Yes. IDEA defines intellectual disability as significantly subaverage general intellectual functioning, existing concurrently with deficits in adaptive behavior and manifested during the developmental period, that adversely affects a child’s educational performance.⁠¹² In 2022 to 2023, 7.5 million students aged 3 to 21 were served under IDEA, and students with intellectual disabilities made up 6% of them.⁠¹³

IDEA keeps intellectual disability apart from a specific learning disability: a learning disability does not include learning problems that are primarily the result of an intellectual disability.⁠¹² See also IEPs and 504 plans.

How does a school evaluation for intellectual disability work?

A parent or the school can request an initial evaluation, which must be completed within 60 days of the parent’s consent, or within the state’s own timeline if it sets one.⁠²⁵ The school must use a variety of tools and may not use any single measure as the sole criterion for deciding that a child has a disability or what program the child needs.⁠²⁶

What services can an IEP include for intellectual disability?

Specialized instruction plus related services. IDEA’s list includes speech-language pathology, psychological services, physical and occupational therapy, recreation and counseling, when a child needs them to benefit from special education.⁠³² Occupational therapy under IDEA includes improving a child’s ability to perform tasks for independent functioning.⁠³²

When does transition planning start?

No later than the first IEP in effect when the child turns 16, or younger if the IEP team decides. From then on, the IEP must include measurable goals for training, education, employment and, where appropriate, independent living, and the services needed to reach them.⁠³³ Many IEP teams for students with intellectual disabilities start earlier, because the sooner planning begins, the more can be done before the student leaves secondary school.⁠³¹

How can families support a child with intellectual disability?

With supports matched to the child’s strengths and needs at home, at school and in the community. The APA lists early intervention, special education, family support such as respite care, transition services, vocational programs and treatment of co-occurring conditions among the services that help.⁠³ With proper support, people with intellectual disabilities are capable of successful, productive roles in society.⁠³

What does early intervention offer children under 3?

Children under 3 are evaluated through their state’s early intervention system, and no doctor’s referral or medical diagnosis is needed to call.⁠²⁴ Under IDEA Part C, the evaluation and assessment are carried out at public expense with no fees to parents; a state may charge sliding fees for services, but a family’s inability to pay cannot delay or deny them.⁠³⁴ Parents are named as primary referral sources.⁠³⁵ More on early intervention and private therapy.

Which therapies help children with intellectual disability?

• Communication. speech-language pathology works on communication; where speech is limited, a child may communicate through gestures, signs or aided systems such as AAC.⁠^6,18
• Daily living. occupational therapy works on a child’s ability to perform tasks for independent functioning.⁠³²
• Movement. physical therapy is available as a related service when a child needs it to benefit from special education.⁠³²

How can adaptive skills be taught at home?

Explicitly, and in small steps. The Center for Parent Information and Resources suggests teaching daily care skills such as dressing, feeding and grooming, giving chores that suit the child’s age, attention span and abilities, and breaking each job into smaller steps.⁠³¹ The APA’s tips for parents include encouraging independence and responsibility and looking for social, recreational and sports activities such as Special Olympics.⁠³

What can adult life look like with an intellectual disability?

It varies with the support a person needs. With appropriate support, many adults with mild intellectual disability hold jobs, keep independence in daily life, and drive or use public transportation; adults with moderate intellectual disability can develop meaningful relationships and relative independence in self-care with ongoing support.⁠⁶ Current approaches emphasize full community inclusion, self-direction, and respect for the person’s own desires and interests.⁠⁴

Frequently Asked Questions

Sources

1. American Psychiatric Association. Intellectual Disability (DSM-5 fact sheet). 2013. Checked October 11, 2026.
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   “Intellectual disability (intellectual developmental disorder) as a DSM-5 diagnostic term replaces” the term “used in previous editions of the manuals”. “While intellectual disability does not have a specific age requirement, an individual’s symptoms must begin during the developmental period and are diagnosed based on the severity of deficits in adaptive functioning.” “DSM-5 emphasizes the need to use both clinical assessment and standardized testing of intelligence when diagnosing intellectual disability, with the severity of impairment based on adaptive functioning rather than IQ test scores alone. By removing IQ test scores from the diagnostic criteria, but still including them in the text description of intellectual disability, DSM-5 ensures that they are not overemphasized as the defining factor of a person’s overall ability, without adequately considering functioning levels. This is especially important in forensic cases.” “intellectual disability is considered to be approximately two standard deviations or more below the population, which equals an IQ score of about 70 or below.” “The American Psychiatric Association (APA) will publish DSM-5 in 2013”.
2. American Association on Intellectual and Developmental Disabilities. Defining Criteria for Intellectual Disability. AAIDD. Checked October 11, 2026.
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   “Intellectual disability is a condition characterized by significant limitations in both intellectual functioning and adaptive behavior that originates before the age of 22.” Intellectual functioning, also called intelligence, “refers to general mental capacity, such as learning, reasoning, problem solving, and so on.” “Generally, an IQ test score of around 70 or as high as 75 indicates a significant limitation in intellectual functioning.” “The condition originates during the developmental period, which is defined as before the age of 22. Intellectual disability is one of several conditions known collectively as developmental disabilities.” The AAIDD lists the “Diagnostic Adaptive Behavior Scale (DABS)”. “Professionals should also consider linguistic diversity and cultural differences in the way people communicate, move, and behave.”
3. American Psychiatric Association. What is Intellectual Disability? Physician review March 2024. Checked October 11, 2026.
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   “Intellectual disability refers to neurodevelopmental conditions that affect functioning in two areas”: “Cognitive functioning, such as learning, problem solving and judgement” and “Adaptive functioning, activities of daily life such as communication skills and social participation”; “typically before age 18 years for diagnosis”. “Intellectual disability affects about 1% of the population, and of those about 85% have mild intellectual disability. In high-income countries, 2–3% of children have an intellectual disability.” “While a specific full-scale IQ test score is no longer required for diagnosis, standardized testing is used as part of diagnosing the condition. A full-scale IQ score of around 70 to 75 indicates a significant limitation”; “scores on subtests can vary considerably”; “clinical judgment is needed”; diagnosis “requires a score of two or more standard deviations below the population norm ... on a standardized measure of adaptive skills such as the vineland adaptive behavior scales”; adaptive functioning “is assessed through standardized measures with the individual and interviews with others, such as family members, teachers and caregivers”. Domains: “Conceptual – language, reading, writing, math, reasoning, knowledge, memory”; “Social – empathy, social judgment, communication skills, the ability to follow rules and the ability to make and keep friendships”; “Practical – independence in areas such as personal care, job responsibilities, managing money, recreation, and organizing school and work tasks”. Causes: “a genetic syndrome, such as Down syndrome or Fragile X syndrome ... an illness such as meningitis, whooping cough or measles; may result from head trauma during childhood; or may result from exposure to toxins such as lead or mercury”; “infection during pregnancy and problems at birth, such as not getting enough oxygen”. “Intellectual disability is a life-long condition. However, early and ongoing intervention may improve functioning”; services include “Early intervention (infants and toddlers)”, “Special education”, “Family support (for example, respite care support groups for families)”, “Transition services from childhood to adulthood” and “Vocational programs”; “With proper support, people with intellectual disabilities are capable of successful, productive roles in society.” “A diagnosis often determines eligibility for services and protection of rights, such as special education services and home and community services.” Co-occurring: “autism spectrum disorder, cerebral palsy, epilepsy, attention-deficit hyperactivity disorder, impulse control disorder, and depression and anxiety disorders”; “recognizing depression in an individual with limited verbal ability”. Tips: “Encourage independence and responsibility.” “Look for opportunities in your community for social, recreational and sports activities (such as Best Buddies or Special Olympics).” References: “The term intellectual disability used in DSM-5-TR replaces” the earlier term; “The majority of people, 68%, have IQ scores between 85 and 115.”
4. American Association on Intellectual and Developmental Disabilities. FAQs on Intellectual Disability. AAIDD. Checked October 11, 2026.
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   “The 12th edition of the AAIDD manual was published in 2021.” “ID is a developmental disability. Each person with ID will have their own strengths and weaknesses”; “Clinical judgment plays an important role in all aspects of the determination of ID.” “a full scale IQ standard score of approximately 2 (or more) standard deviations below the mean”; adaptive behavior “approximately 2 (or more) standard deviations below the mean ... in one or more of the following domains: conceptual, social, or practical skills”; “Onset of both of the above limitations during the developmental period, which means that significant limitations in both intellectual functioning and adaptive behavior in the individual have manifested before the age of 22.” “all test results must be interpreted within the context of their administration and any potential sources of testing error”. Causes relate to “risk factors (biomedical, social, behavioral, and educational) and the timing of exposure (before a person is born, around the time of their birth, and after the person is born)”. “In its 12th edition of the Manual, AAIDD defines the end of the developmental period as age 22 based on contemporary research that has shown that important brain development continues into our 20s. Additionally ... this age of onset is also consistent the standards used for a diagnosis of ID in the DSM-5 and the ICD-11 and for service eligibility by the US Social Security Administration.” “The change in the operational definition of developmental period is not expected to impact prevalence rates because the vast majority of diagnoses of ID are” “made in early childhood”; it “will enable the accurate diagnosis of the small percentage of individuals who are identified nearer to the end of the developmental period”. “The overarching reason for evaluating and classifying ID is to be able to tailor a personalized set of supports”. “Current approaches to services and supports emphasize promoting full community inclusion, enhancing self-direction”; supports “are expected to respect the desires and interests of people with ID”.
5. American Association on Intellectual and Developmental Disabilities. Historical Context. AAIDD. Checked October 11, 2026.
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   “The three leading scholarly and clinical organizations concerned with this condition, the AAIDD, American Psychiatric Association, and World Health Organization have been in agreement for more than 50 years that the three essential elements for this condition are: Substantial limitations in intellectual functioning; Substantial limitations in adaptive behavior; Onset during the developmental period”. Older documents that use the former term “can be understood within their historical or legal contexts”.
6. Patel DR, Cabral MD, Ho A, Merrick J. A clinical primer on intellectual disability. Translational Pediatrics. 2020;9(Suppl 1):S23–S35. PMID 32206581. Checked October 11, 2026.
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   According to the DSM, “the deficits in intellectual function include reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience”; “Deficits in adaptive functioning result in failure to meet developmental and sociocultural standards for personal independence and social responsibility.” “A diagnosis of intellectual disability should not be based solely on the results of tests”. Mild: “Eighty-five percent ... less likely to be recognized to have ID before 5–6 years of age”; “They can reach academic skills equivalent to 4th–5th grade level”; “can be sufficiently skilled as adults to be gainfully employed and able to maintain independence in daily life activities”; “They can also learn to drive and use public transportation.” “need intermittent support in daily living activities such as self-care, shopping, food preparation and money management”. Moderate: “About 10%”, “recognized to have an ID by 3–5 years of age”; “The rate of acquisition of basic language skills is slow”; “academic skills equivalent to early elementary school grade level”; “With ongoing support, persons with moderate ID can develop meaningful family and personal relationships”; “need substantial ongoing support”; “can attain relative independence in self-care”. Severe: “About 4%”, “by 3 years of age or earlier”; “communication may be limited to use of single words or phrases”; “Their communication ability may be improved with use of augmentative communication methods.” “The social interactions and relationships ... are largely limited to immediate family members and care takers.” “need extensive, regular, consistent, and lifetime support”. Profound: “Approximately 1%”, “recognized by 2 years of age”; “need high intensity, pervasive support across all environments”; “significant limitations in self-care, continence, communication and mobility”; “may respond to familiar persons or caretakers with gestures and facial emotional cues”. “in persons with severe intellectual disability, a specific underlying genetic, biological or neurological can be identified in more than 75% of cases”; mild: “Major risk factors ... are environmental and psychosocial, and include low socioeconomic status, residence in low-income countries, low maternal education, malnutrition, and inadequate access to healthcare”. “Hearing and vision should be assessed in all children”; testing should “accommodate for any motor, behavioral, or language variations”. Reasons for an etiological diagnosis: “Anticipate complications; Identify treatable cause; ... Facilitate research; Plan intervention services; Access support services; Provide genetic counseling”. “Early identification of treatable inborn errors of metabolism is important to improve long-term outcomes”; “Improved prenatal care, improved access to maternal-child health, newborn screening for inborn errors of metabolism, and improved immunization rates, contribute to reduced rates of intellectual disability”. “The level of adaptive functioning and the intensity of supports needed are the main criteria used to categorize intellectual disability levels of severity.” “IQ alone is not considered sufficient criteria to determine whether a person should be considered to have an intellectual disability nor to determine its severity.” “Measured IQ ... may or may not necessarily correlate with the level of adaptive functioning”. “The standardized tests ... are generally difficult to administer in very young children”. “Severe and profound ID are differentiated primarily based on differences in limitations of adaptive behavior because the validity and reliability of standardized tests of intelligence are not clearly established” at the lowest levels.
7. National Center for Health Statistics. Diagnosed Developmental Disabilities in Children Aged 3–17 Years: United States, 2019–2021. NCHS Data Brief No. 473, July 2023 (Zablotsky B, Ng AE, Black LI, Blumberg SJ). Checked October 11, 2026.
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   “No significant change in the prevalence of diagnosed intellectual disability was observed during 2019–2021 (1.70% in 2019, 2.20% in 2020, and 1.65% in 2021).” “the prevalence of diagnosed intellectual disability was higher in boys (2.31%) than girls (1.37%)”; “The prevalence of intellectual disability increased with age, from 1.39% for children aged 3–7 years to 2.35% for children aged 13–17 years.”
8. Eunice Kennedy Shriver National Institute of Child Health and Human Development. What causes intellectual and developmental disabilities (IDDs)? NICHD. Checked October 11, 2026.
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   “most cases of Rett syndrome are caused by a change in the” MECP2 gene; “Down syndrome results from having an extra copy or part of a copy of chromosome 21”; “exposure to alcohol while in the womb can result in fetal alcohol spectrum disorder”; “Infections during pregnancy: for example, infants whose mothers had cytomegalovirus during pregnancy may have hearing, vision, and neurological problems”; “Problems during childbirth”; “Traumatic Brain Injury (TBI)”; “Preterm birth”.
9. Moeschler JB, Shevell M; Committee on Genetics. Comprehensive evaluation of the child with intellectual disability or global developmental delays. Pediatrics. 2014;134(3):e903–e918. PMID 25157020. Checked October 11, 2026.
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   The abstract: “Chromosome microarray is designated as a first-line test and replaces the standard karyotype and fluorescent in situ hybridization subtelomere tests for the child with intellectual disability of unknown etiology. Fragile X testing remains an important first-line test.” In the text: “The term GDD is reserved for younger children (ie, typically younger than 5 years), whereas the term ID is usually applied to older children for whom IQ testing is valid and reliable.”
10. Manickam K, McClain MR, Demmer LA, Biswas S, Kearney HM, Malinowski J, Massingham LJ, Miller D, Yu TW, Hisama FM; ACMG Board of Directors. Exome and genome sequencing for pediatric patients with congenital anomalies or intellectual disability: an evidence-based clinical guideline of the American College of Medical Genetics and Genomics (ACMG). Genetics in Medicine. 2021;23(11):2029–2037. PMID 34211152. Checked October 11, 2026.
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    The abstract: “Compared with standard genetic testing, ES/GS has a higher diagnostic yield and may be more cost-effective when ordered early in the diagnostic evaluation.” “We strongly recommend that ES/GS be considered as a first- or second-tier test for patients with CA/DD/ID.”
11. Totsika V, Liew A, Absoud M, Adnams C, Emerson E. Mental health problems in children with intellectual disability. The Lancet Child & Adolescent Health. 2022;6(6):432–444. PMID 35421380. Checked October 11, 2026.
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    The abstract: “Approximately 40% of children with intellectual disability present with a diagnosable mental disorder, a rate that is at least double that in children without intellectual disability.”
12. Electronic Code of Federal Regulations. 34 CFR 300.8 Child with a disability. IDEA Part B regulations. Checked October 11, 2026.
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    (c)(6): “Intellectual disability means significantly subaverage general intellectual functioning, existing concurrently with deficits in adaptive behavior and manifested during the developmental period, that adversely affects a child’s educational performance.” (c)(10)(ii): “Specific learning disability does not include learning problems that are primarily the result of visual, hearing, or motor disabilities, of intellectual disability, of emotional disturbance, or of environmental, cultural, or economic disadvantage.”
13. National Center for Education Statistics. Students With Disabilities. Condition of Education. Checked October 11, 2026.
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    “In 2022–23, the number of students ages 3–21 who received special education and/or related services under the Individuals with Disabilities Education Act (IDEA) was 7.5 million”; “Students with developmental delays, intellectual disabilities, and emotional disturbances accounted for 7, 6, and 4 percent of students served under IDEA, respectively.”
14. U.S. Government Publishing Office. Public Law 111-256 (Rosa’s Law). 124 Stat. 2643, October 5, 2010. “An Act To change references in Federal law to mental retardation to references to an intellectual disability”; “This Act may be cited as ‘‘Rosa’s Law’’”; the IDEA sections are amended by inserting “with intellectual disabilities”. Checked October 11, 2026.
15. American Association on Intellectual and Developmental Disabilities. Adaptive Behavior. AAIDD. Checked October 11, 2026.
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    “Adaptive behavior is the collection of conceptual, social, and practical skills that all people learn in order to function in their daily lives”; “Adaptive behavior is a different concept than intelligence. Adaptive behaviors are learned behaviors that reflect an individual’s social and practical competence to meet the demands of everyday living.” “Making a phone (or video) call is an example of adaptive behavior that changed over time. The skills needed to make a call today are very different from the skills that were required 20 years ago.”
16. Eunice Kennedy Shriver National Institute of Child Health and Human Development. About Intellectual and Developmental Disabilities (IDDs). NICHD. “Intellectual disability starts any time before a child turns 18 and is characterized by differences with both: Intellectual functioning or intelligence ... and Adaptive behavior, which includes everyday social and life skills.” Checked October 11, 2026.
17. Social Security Administration. 12.00 Mental Disorders: Adult. Disability Evaluation Under Social Security. Intellectual disorder (12.05) “is characterized by significantly subaverage general intellectual functioning, significant deficits in current adaptive functioning, and manifestation of the disorder before age 22.” Checked October 11, 2026.
18. American Speech-Language-Hearing Association. Intellectual Disability. Practice Portal. Checked October 11, 2026.
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    “Diagnosis of ID is not made by a speech-language pathologist (SLP). However, information gathered during SLP evaluation and treatment may be useful to medical professionals who may diagnose ID.” “AAIDD identifies the level of ID based on the level of supports needed for an individual to successfully function in activities of daily living. These levels of support are described as intermittent, limited, extensive, or pervasive. The DSM-5 uses severity level to define an individual with ID as mild, moderate, severe, or profound.” “One of the major shifts in the early 1980s was a move toward person-first language, reflecting the idea that the disability does not define the person.” “Terminology continues to evolve, with some individuals preferring identity-first language”; ASHA “aligns with the Disability section of the 7th edition of the American Psychological Association (2020) style manual, which says to use the terminology preferred by the individual.” Communication “may occur through nonspoken means only”, “such as gestures, signs, facial expressions, or aided systems (e.g., AAC)”.
19. Centers for Disease Control and Prevention. Down Syndrome. January 8, 2026. “Down syndrome is a condition in which a person has an extra copy of chromosome 21.” “the extra chromosome changes how their body and brain develop”. Checked October 11, 2026.
20. Centers for Disease Control and Prevention. About Fragile X Syndrome. July 20, 2026. “Fragile X syndrome (FXS) is a genetic disorder and one of the most common causes of inherited intellectual disability.” “A diagnosis of FXS can be helpful to the family because it can provide a reason for a child’s intellectual disabilities and behavior problems.” Checked October 11, 2026.
21. Centers for Disease Control and Prevention. About Fetal Alcohol Spectrum Disorders (FASDs). CDC. A person with an FASD might have “Intellectual disability or low IQ”. “FASDs are preventable if a developing baby is not exposed to alcohol.” Checked October 11, 2026.
22. MedlinePlus Genetics. Phenylketonuria. National Library of Medicine. “If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.” Checked October 11, 2026.
23. Centers for Disease Control and Prevention. About Newborn Dried Blood Spot Screening. CDC. “Every state in the United States has a public health program that screens babies for many serious conditions. Shortly after a baby is born, a health professional takes a few drops of blood from the baby’s heel”. Checked October 11, 2026.
24. Centers for Disease Control and Prevention. Concerned About Your Child’s Development? Learn the Signs. Act Early., February 17, 2026. Checked October 11, 2026.
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    “if you think there could be a problem with the way your child plays, learns, speaks, acts, and moves talk to your child’s doctor and share your concerns. Don’t wait.” The AAP recommends screening “for autism at 18 and 24 months or whenever a parent or provider has a concern”. Specialists include “Developmental pediatricians”, “Child neurologists” and “Child psychologists or psychiatrists”. “call your state’s public early childhood system to request a free evaluation”; “You do not need to wait for a doctor’s referral or a medical diagnosis to make this call.” Under 3, “contact your local early intervention system”; at 3 or older, “call any local public elementary school”.
25. Electronic Code of Federal Regulations. 34 CFR 300.301 Initial evaluations. IDEA Part B regulations. Checked October 11, 2026.
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    “either a parent of a child or a public agency may initiate a request for an initial evaluation to determine if the child is a child with a disability”; it “Must be conducted within 60 days of receiving parental consent for the evaluation; or ... If the State establishes a timeframe within which the evaluation must be conducted, within that timeframe”.
26. Electronic Code of Federal Regulations. 34 CFR 300.304 Evaluation procedures. IDEA Part B regulations. Checked October 11, 2026.
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    The agency must “Not use any single measure or assessment as the sole criterion for determining whether a child is a child with a disability and for determining an appropriate educational program for the child”. Assessments “Are selected and administered so as not to be discriminatory on a racial or cultural basis” and “Are provided and administered in the child’s native language or other mode of communication”; they “include those tailored to assess specific areas of educational need and not merely those that are designed to provide a single general intelligence quotient”.
27. Einfeld SL, Ellis LA, Emerson E. Comorbidity of intellectual disability and mental disorder in children and adolescents: a systematic review. Journal of Intellectual & Developmental Disability. 2011;36(2):137–143. PMID 21609299. Checked October 11, 2026.
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    The abstract: “Collectively, these studies demonstrate rates of comorbidity for children and adolescents between 30 and 50% with a relative risk of mental disorder associated with intellectual disability ranging from 2.8–4.5.”
28. Dell’Armo K, Tasse MJ. How intellectual disability may bias psychologists’ clinical impressions: an examination of diagnostic overshadowing. Psychological Assessment. 2025;37(4):161–171. PMID 40167540. Checked October 11, 2026.
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    The abstract: diagnostic overshadowing is “a phenomenon in which a diagnosis of intellectual disability (ID) is so salient that it ‘overshadows’ the presence of other mental health conditions, whose symptoms are falsely attributed to the ID”; “Three hundred eighteen licensed psychologists participated”; “the magnitude of this difference was small”; “psychologists do recognize the presence of a mental health condition in a person with ID, but there may be some reduced accuracy in the specific diagnosis that is made.”
29. Maulik PK, Mascarenhas MN, Mathers CD, Dua T, Saxena S. Prevalence of intellectual disability: a meta-analysis of population-based studies. Research in Developmental Disabilities. 2011;32(2):419–436. PMID 21236634. Checked October 11, 2026.
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    The abstract: “The prevalence of intellectual disability across all 52 studies included in the meta-analysis was 10.37/1000 population.” “The highest rates were seen in countries from low- and middle income countries.” “Prevalence was higher among studies based on children/adolescents, compared to those on adults.”
30. American Psychological Association. Disability. APA Style, bias-free language guidelines. Checked October 11, 2026.
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    “Language should be selected with the understanding that the expressed preference of people with disabilities regarding identification supersedes matters of style.” “In person-first language, the person is emphasized, not the individual’s disabling or chronic condition”; “use ‘people with intellectual disabilities’”. Avoid “negativistic terms that imply restriction”, “excessive and negative labels” and “terms that can be regarded as slurs”.
31. Center for Parent Information and Resources. Intellectual Disability. Disability fact sheet. Checked October 11, 2026.
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    “Until Rosa’s Law was signed into law by President Obama in October 2010, IDEA used the term” the former term; “The definition itself, however, did not change.” “IDEA requires that, at the latest, transition planning for students with disabilities must begin no later than the first IEP to be in effect when they turn 16. The IEP teams of many students with intellectual disabilities feel that it’s important for these students to begin earlier than that.” “the sooner transition planning begins, the more can be accomplished before the student leaves secondary school”. Tips for parents: “Encourage independence in your child. For example, help your child learn daily care skills, such as dressing, feeding him or herself, using the bathroom, and grooming.” “Give your child chores. Keep her age, attention span, and abilities in mind. Break down jobs into smaller steps.”
32. Electronic Code of Federal Regulations. 34 CFR 300.34 Related services. IDEA Part B regulations. Checked October 11, 2026.
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    “Related services means transportation and such developmental, corrective, and other supportive services as are required to assist a child with a disability to benefit from special education, and includes speech-language pathology and audiology services, interpreting services, psychological services, physical and occupational therapy, recreation, including therapeutic recreation, early identification and assessment of disabilities in children, counseling services”; occupational therapy includes “Improving ability to perform tasks for independent functioning if functions are impaired or lost”.
33. Electronic Code of Federal Regulations. 34 CFR 300.320 Definition of individualized education program. IDEA Part B regulations. Checked October 11, 2026.
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    (b): “Beginning not later than the first IEP to be in effect when the child turns 16, or younger if determined appropriate by the IEP Team, and updated annually, thereafter, the IEP must include” “(1) Appropriate measurable postsecondary goals based upon age appropriate transition assessments related to training, education, employment, and, where appropriate, independent living skills; and (2) The transition services (including courses of study) needed to assist the child in reaching those goals.”
34. Electronic Code of Federal Regulations. 34 CFR 303.521 System of payments and fees. IDEA Part C regulations. Checked October 11, 2026.
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    Functions “that must be carried out at public expense, and for which no fees may be charged to parents” include “Evaluation and assessment”; a State may set a “schedule of sliding or cost participation fees that may be charged to the parent for early intervention services”, with an assurance that “The inability of the parents of an infant or toddler with a disability to pay for services” does not result in a “delay or denial of services”.
35. Electronic Code of Federal Regulations. 34 CFR 303.303 Referral procedures. IDEA Part C regulations. (c): “primary referral sources include” ... “(3) Parents, including parents of infants and toddlers”. Checked October 11, 2026.

Medical disclaimer. This page is for general educational purposes and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your child.