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What Can You Learn from IQ Tests?

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By Susan Baum, Ph.D.

The Wechsler Intelligence Scale for Children (WISC IV) is one of the most heavily weighted tests in your child’s evaluation for learning disabilities—and one of the most misunderstood. The test provides an overall IQ (intelligence quotient) generated from four composite indexes. These are:

  • Verbal Comprehension Index (VCI),
  • Perceptual Reasoning Index (PRI),
  • Working Memory Index (WMI) and the
  • Processing Speed Index (PSI).

Each index is made up of three or four subtests. Each purports to measure a different aspect of intelligence. The benefit of IQ tests for children with LD is not in the aggregate scores, but in the analysis of subtest scores, which provide insights into a child’s strengths and weaknesses.


Although high overall IQ scores are associated with success in school, they do not equate with intelligence and can be misleading for children with LD. By averaging subtest scores, strengths and weaknesses are masked and overall IQ results are depressed.


Case Study

Debra has a full IQ score of 117, which is considered high average. Her Verbal Comprehension Index (VCI) of 144 indicates that she fares better than 99.9% of age mates on tasks involving reading, listening and conceptualization. This score is indicative of academic giftedness. While her scores on the Perceptual Reasoning Index  (98) and on the Working Memory Index (99) both fall in the average range, they are significantly lower than her ability to conceptualize and may compromise her ability to produce work commensurate with her conceptualization abilities. A score of 88 (21st percentile) on the Processing Speed Index further inhibits her ability to achieve up to her potential. In this area Debra shows severe deficits. In sum, her scores suggest that Debra has high-average overall intelligence. However an analysis of her index scores shows she has abundant strengths along with significant weaknesses, which may indicate that she has learning disabilities.

Like many kids with LD, Debra struggles in areas that rely on working memory, attention, and processing speed.  It is obvious that her production will lag behind her superior verbal abilities. Lower scores in Perceptual Reasoning often predict issues with executive functioning symptomatic of students with nonverbal learning disabilities.

Debra’s profile of strengths as evidenced in her high VCI score and weaknesses especially in PSI allow her to be identified as both gifted and LD. Her best chance to overcome her difficulties will be to capitalize on her analytic skills, the area of her greatest strength.