Intellectual Disability



Intellectual disability involves impairments of general mental abilities that impact functioning.  It is characterized by deficits in
  • intellectual functioning (learning, reasoning)
  • adaptive functioning that limits function in activities of daily life (communication and independent living) 
Intellectual disability affects approximately 1 percent of the population and of those, about 85% have mild intellectual disability.

Diagnosing Intellectual Disability

Intellectual disability is identified by impairments in adaptive functioning in three areas: ·        

– language, reading, writing, math, reasoning, knowledge, memory

Social –   empathy, social judgment, interpersonal communication skills,
                  the ability to follow rules and to make and retain friendships
Practical – self-management in areas such as personal care, job
                  responsibilities, money management, recreation, and organizing
                  school and work tasks

Both clinical assessment and standardized testing of intellectual functioning are used to diagnose intellectual disability. Full scale IQ test scores are no longer required for diagnosis, however, standardized testing is required as part of the diagnostic assessment. Although a full scale IQ score of around 70 to 75 indicates a significant limitation in intellectual functioning, the IQ score must be interpreted clinical in the context of impairments in general mental abilities. Moreover, subtests scores can vary considerably so that the full scale IQ score may not accurately reflect overall intellectual functioning.

Adaptive functioning is assessed with standardized measures with the individual and interviews with others such as family members, teachers, and caregivers. The symptoms of intellectual disability must begin during childhood or adolescence. Delayed motor, language and social milestones may be identifiable by age 2. However, mild levels may not identifiable until school age when a child may have difficulty with academics.


There are many different causes of intellectual disability. It can be associated with a genetic syndrome, such as Down syndrome and Fragile X syndrome. It may develop following 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.  Brain malformation, maternal disease, environmental influences (alcohol, drugs, or other toxins), a variety of labor and delivery-related events, infection during pregnancy, and problems at birth, such as not getting enough oxygen, may contribute to intellectual disability.


Intellectual disability is generally life-long, though early and ongoing intervention may improve functioning and enable the person to thrive throughout their lifetime. It may also be influenced by underlying medical or genetic conditions and co-occurring conditions. The American Association of Intellectual and Developmental Disabilities (AAIDD) stresses the “the overarching reason for evaluating and classifying individuals with intellectual disabilities is to tailor supports for each individual, in the form of a set of strategies and services provided over a sustained period.” Once a diagnosis is made, the focus is on looking at the individual’s strengths and needs and the supports he or she needs to function at home, in school/work, and in the community. Services for people with intellectual disabilities and their families provide support to allow full inclusion in the community.

These services may include:
  • Early intervention 
  • Special education 
  • Family support (for example, respite care) 
  • Transition services 
  • Vocational programs 
  • Day programs 
  • Residential options 
  • Case management 

Under federal law (Individuals with Disabilities Education Act, IDEA) Early Intervention services work to identify and help infants and toddlers with disabilities. Federal law also requires that special education and related services are available free to every eligible child with a disability, including intellectual disability. In addition, supports can come from family, friends, co-workers, community members, or from a service system.  Job coaching is an example of a support provided by a service system. 

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 conditions Some mental, neurodevelopment, medical, and physical conditions frequently co-occur in individuals with intellectual disability including cerebral palsy, epilepsy, and mental and neurodevelopmental disorders such as ADHD, depression, and anxiety disorders, and autism spectrum disorder.

Tips for parents

  • Learn about your child’s disability
  • Connect with other parents of children with disabilities
  • Be patient, learning may come slower for your child
  • Encourage independence and responsibility
  • Look for opportunities in your community for social, recreational, and sports activities

*The term Intellectual Disability used in DSM-5 replaces “mental retardation” used previously. 

For More Information

American Association on Intell
ectual and Developmental Disabilities  

The Arc

National Dissemination Center for Children with Disabilities NICHCY