On WISC and WIAT

.:I recently read a question about the differences between the WISC and the WIAT and why a child might do better on one than the other – particularly why better on the WIAT. So, I decided to write a post.

The WISC (Wechsler Intelligence Scale for Children) is an intelligence test.  There’s very little agreement as to exactly what intelligence is, but the WISC-V attempts to measure five broad areas, called indexes:

  • Verbal comprehension
  • Visual spatial ability
  • Fluid reasoning
  • Working memory
  • Processing speed

these can be combined in various ways, including to form a full scale IQ.  For kids with NLD or other LD, it is usually necessary to look at all the indexes and even the individual subtests, because LD people often have very scattered skills.

The WIAT (Wechsler Individual Achievement Test) is intended to measure academic achievement.

Scores on achievement and intelligence tests are correlated in mainstream populations. But, even in mainstream populations, the correlations are far from perfect.  So, what might account for discrepancies?

Reasons that apply to all children:

  • Mood and so on on that day  (e.g. mood, tiredness, hunger, etc)
  • Rapport with the person administering the test
  • Skill of the person
  • The room the test was given in

Reasons that apply more to LD children:

  • Children with NLD often have relatively few problems with academics. Of the five indices of the WISC, they tend to do worst on visual spatial ability and best on verbal comprehension.  This leads to relatively good academic performance, especially if you exclude math.  But the math on the WIAT consists of numerical operations and math reasoning, and these may be relative areas of strength within an overall math weakness. In any case, math is only one of four areas tested on the WIAT.
  • Other LDs are different, often just the opposite.

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