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REGARDING LEARNING DISABILITIES
(INFORMATION FOR PARENTS)

cont.

ASSESSMENT

This will vary from state to state, although every state is expected to adhere to federal standards. One method that some diagnosticians use is to examine differences between verbal and nonverbal intelligence on tests such as the Wechsler Intelligence Scale for Children-Third Edition (WISC-III). On the WISC-III, this would mean comparing the Verbal IQ with the Performance IQ. One problem with this approach is that Dr. Wechsler and his followers never intended the Verbal and Performance scales to be measuring separate and discriminable aspects of intelligence. They are both different manifestations of general intelligence. The distinction between verbal and nonverbal is therefore rather arbitrary and is not even theory-driven.

Another method of evaluating LD problems is to examine subtest "scatter" (i.e., differences in subtest scores) on tests like the WISC-III. This is wrong headed for several reasons. Among them:

1. IQ tests presumably measure cognitive ability, not academic prowess;
2. subtest scatter is common and "statistically significant" differences in scores may not have any practical relevance;
3. the DSM-III-R requires a more thorough evaluation of cognitive AND academic functioning; etc.

The most accepted practice is to compare IQ scores with standard scores on individually administered achievement tests such as the Wechsler Individual Achievement Test (WIAT). Certain states will apply the LD diagnosis when a particular achievement test score is 1.25 standard deviations units lower than the IQ score (a standard deviation is usually 15 points). Thus, a child whose basic reading score is 75, but whose IQ is 98, would be regarded as LD, provided that the reading problem is not secondary to generalized mental impairment (e.g., Mental Retardation), sensory disorders, emotional disturbance, or lack of academic opportunity.

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But the state of the art method for diagnosing learning disabilities is to use sophisticated psychometric properties of tests such as the WIAT in order to derive predicted (expected) achievement scores based on the IQ score. The test manual will tell you, for example, that a child with an IQ of 92 is predicted (expected) to receive certain scores on each of the achievement tests. You then compare the child's ACTUAL achievement scores with her PREDICTED scores on each of the tests. This is the method favored by the DSM-III-R, which stipulates that the academic skill, "as measured by a standardized, individually administered test," is "markedly below the expected level, given the person's schooling and intellectual capacity (as determined by an individually administered IQ test)." The diagnostician would still have to rule out the possible causes of the LD problem which were listed previously, and that skill deficit must be having a demonstrable impact on the child's schoolwork.

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