Information on Five Challenging Disabilities-Intellectual Disability

Although IDEA 2004 provides federal guidelines, each state may have slightly different ways of determining who is eligible for classification under certain categories of disability, and intellectual disability (ID) is a good example of this. While all states require evidence of subaverage IQ and impaired adaptive functioning as part of the eligibility criteria for ID, the actual scores used to determine whether a child qualifies for the program vary from state to state. Parents and teachers are often frustrated to learn that even though a child may qualify for ID status based on IQ and adaptive functioning, the child may not qualify for services under this category if academic skills do not also fall within this specified range. It may also be frustrating if the child moves to a different state and no longer qualifies because the eligibility requirements are different.

We discuss how learning potential or intelligence is calculated based on ability scores relative to age expectations. The majority of classification systems consider an IQ below 70 to be within the ID range. Remember that approximately 2 percent of the population has an IQ score below 70. (You will see in Chapter Seven that 68 percent of the population has an IQ score between 85 and 115; the average IQ score is 100.)

REMEMBER: In order to establish eligibility for those functioning within the range of intellectual disability (ID), it is necessary to determine not only an IQ significantly below the average range, but also provide evidence of adaptive functioning deficits in at least two areas.

The Range of Intellectual Disability   The IQ scores of individuals who are classified as intellectually disabled can range from an IQ of about 70 (plus or minus 5 points of measurement error) to an IQ below 20. There is great variability in the characteristics of children whose scores fall within this wide range. Although the range is large, the vast majority (85 percent) of children with ID fall within the mild range (IQ range from 55 to 75). Children who fall in the lower ranges (IQ less than 40) often have multiple disabilities. IDEA 2004 does not specify different levels of ID, but the DSM-IV-TR (APA, 2000) provides four categories. The percentages of individuals who score in different ranges and the expectations associated with each of the levels of ID (mild, moderate, severe, and profound) are shown in Table 3.3.