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Intellectual Disability

boy writing

(Previously Mental Retardation, also called Intellectual Developmental Disorder)

Intellectual Disabilities (ID) is a term used when a person has significant limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills. These limitations will cause a child to learn and develop more slowly than a typical child. A student with ID has sub average (lower) intelligence. The average score is 100. People scoring below 70 to 75 are considered to have an intellectual disability. This affects intellectual functioning and adversely affects educational performance. Assessment results in the areas of intellectual, academic, and adaptive show consistently low scores. Adaptive behavior (the ability to adjust to a new situation) is impaired. This disability was previously called Mental Retardation (MR).

People with ID can and do learn new skills, but they learn them more slowly. There are varying degrees of intellectual disability, from mild to profound. ID is characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors before the age of 18. It has historically been defined as an Intelligence Quotient (IQ) score under 70. Note: A young child ages 3 through 7, who has been diagnosed as Developmental Delayed in pre-school or early childhood education and who shows a significant delay in cognitive development may be diagnosed as Intellectual Disabled when he or she enters the educational system at age 7 or 8.

Some of the most common signs of intellectual disability are:

  • Rolling over, sitting up, crawling, or walking late
  • Talking late or having trouble with talking
  • Slow to master things like potty training, dressing, and feeding himself or herself
  • Difficulty remembering things
  • Inability to connect actions with consequences
  • Behavior problems such as explosive tantrums
  • Difficulty with problem-solving or logical thinking

Resource from WebMD

What Causes Intellectual Disability?

Anytime something interferes with normal brain development, intellectual disability can result. However, a cause is only known in about 30% of children. The most common causes are:

  • Genetic conditions. These include syndromes like Down syndrome, fragile X syndrome, Williams syndrome/Trisomy 18, Angelman syndrome.
  • Problems during pregnancy. Things that can interfere with fetal brain development include alcohol or drug use (Fatal Alcohol syndrome), malnutrition (extreme celiac disease), certain infections (Reyes syndrome), or preeclampsia.
  • Problems during childbirth. Intellectual disability may result if a baby is deprived of oxygen during childbirth or born extremely premature. (some cases of cerebral palsy)
  • Illness or injury. Infections like meningitis, whooping cough, or the measles can lead to intellectual disability. Severe head injury (traumatic brain injury), near-drowning, extreme malnutrition (Anorexia Nervosa), exposure to toxic substances such as lead, and severe neglect or abuse can also cause it.
girl reading with help from woman


Intellectual disability is the most common developmental disability. Approximately 6.5 million people in the United States have an intellectual disability. More than 545,000 children (ages 6-21) have some level of intellectual disability and receive special education services in public school under this category in IDEA, the nation’s special education law. In fact, 1 in every 10 children who need special education have some form of intellectual disability.

How to Identify and Respond to It

Parents are usually the first to recognize that their child learns new skills slower than their other children learned. Speech may develop slower. Self-help skills such as eating and dressing, also happen at a slower pace. Formal and informal assessments will be used in order to identify a student with an intellectual disability. Some of these assessments include an individual major test of intelligence (IQ) by a qualified examiner. Adaptive behavior information is gathered from parents, observations and oral tests. Students will need early intervention or Special Education and related services.

A child with an intellectual disability can do well in school but is likely to need the individualized help that’s available through special education and related services. The level of help and support that’s needed will depend upon the degree of the intellectual disability involved.

Websites and Other Resources