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Intellectual Disability (ID)

  • Intellectual Disability by James C. Harris-ISBN: 9780195145724 Publication Date: 2010-06-24
  • A Different Kind of Perfect by Bernadette Thomas (Editor); Neil Nicoll (Editor); Cindy Dowling-ISBN: 9781590303078 Publication Date: 2006-09-12
  • Why Are You Looking at Me? by Lisa Tompkins-ISBN: 9781481711388 Publication Date: 2013-01-01
  • I Can, Can You? by Marjorie W. Pitzer-ISBN: 9781890627577 Publication Date: 2004-05-01
  • Don't Call Me Special by Pat Thomas; Lesley Harker (Illustrator)-ISBN: 9780764121180 Publication Date: 2002-05-01
  • Tru Confessions by Janet Tashjian-ISBN: 9780312372736 Publication Date: 2007-10-16


Intellectual disability (ID) is below-average cognitive ability with significant limitations in adaptive skills areas. 


The diagnosis of ID is made based on testing of cognitive and adaptive skills. Cognitive skills are things like memory, reasoning, and learning. Adaptive skills are those skills needed in daily live, such as self-care, home living, social skills, leisure skills, health and safety, community participation and employment. In order to have a diagnosis of ID, a child must have below-average cognitive ability (usually defined as an Intelligence Quotient (IQ) of below 70), along with below-average adaptive skills. These deficits must be present before age 18. Because intelligence testing is not reliable in young children, young children often are not diagnosed with ID before school age. Children often first are noted to have developmental delays in language, motor, social, adaptive, or cognitive areas. These children may catch up, may go on to have ID, or may not meet criteria for ID but instead have a domain specific disorder (communication disorder or motor skills disorder).

How Many People Have Intellectual Disability?

Somewhere between 1 and 3 of every 100 Americans have ID.

What Causes Intellectual Disability?

ID can be caused by any condition that impairs development of the brain before birth, during birth, or during the early childhood years. In about 1 of 3 of people with intellectual disabilities, the cause is unknown. The most common known causes of intellectual disabilities are fetal alcohol spectrum disorder (FASD) and genetic conditions including Down syndrome and ID syndrome.

Associated Developmental and Learning Issues

The impact of having an ID varies considerably, just as the range of abilities varies considerably among all people. Children may take longer to learn to speak, walk and take care of their personal needs, such as dressing or eating. It may take longer to learn in school. As adults, some people are able to lead independent lives in the community, while others require more formal supports.

There is no cure for ID, but with treatment and supports, those with intellectual disabilities can lead satisfying lives in the community. 

Associated Health Conditions 

For a variety of reasons, certain health conditions are more common in children with intellectual disability. It is important that these are recognized and treated. A child with ID who is physically healthy is more likely to do well in school and in other treatments. This contributes to more independence, better daily functioning, and better quality of life. 

  • Dysmenorrhea (painful menstruation)
  • Feeding and growth problems
  • GI problems (gastroesophageal reflux disease (GERD), constipation)
  • Musculoskeletal problems including hypotonia and scoliosis
  • Oral health problems
  • Otitis Media (ear infections)
  • Seizures
  • Sleep problems
  • Vision and hearing problems

Associated Behavioral Conditions

Some, but not all, children with ID have behavioral challenges such as

  • ADHD
  • Aggression, self-injury
  • Anxiety
  • Tantrums


Visit the Intellectual Disability LibGuide for resources.