The Diagnosis of Intellectual Disabilities

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The first indication of an intellectual disability (ID, formerly mental retardation) is usually a child's physical and behavioral characteristics. Once an intellectual disability is suspected, a formal evaluation and assessment begins.

The evaluation begins with a complete physical examination. A thorough review of medical history identifies any physical or medical causes of the troubling symptoms. Some medical conditions that cause ID can be treated effectively. However, even reversible conditions require immediate attention. This is because prompt attention reduces the risk of lasting brain damage. Hyperthyroidism is an example of a treatable condition that can cause an intellectual disability if not treated promptly. If a neurological cause of the symptoms is suspected, the child is referred to a neurologist for further testing. The many causes of ID are discussed in another section.


Previously, we reviewed intellectual disabilities are defined by two major symptoms. First, there are limitations in intellectual functioning (mental abilities). Second, there are limitations in adaptive functioning or life skills. These life skills include conceptual, social, and practical skills. Therefore, a medical evaluation is just the beginning of the assessment process. A thorough assessment usually includes the following:

  • comprehensive medical exam;
  • possible genetic and neurological testing;
  • social and familial history;
  • educational history;
  • psychological testing to assess intellectual functioning;
  • testing of adaptive functioning;
  • interviews with primary caregivers;
  • interviews with teachers;
  • social and behavioral observations of the child in natural environments

As mentioned, intellectual functioning and adaptive functioning are the primary diagnostic criteria. In the next section, we discuss various tests used to assess intellectual functioning and adaptive functioning. Since significant limitations in these two areas are the defining features of intellectual disabilities, these tests are essential to the diagnostic process.

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