Interesting study about a girl with a 54 point gap on the WISC-R’s verbal and performance scale. When tested at 11, her verbal IQ was 96 and her performance IQ was 150! But when re-tested at age 12, her verbal IQ had jumped to 114 and her performance IQ had tumbled to 126, for only a 12 point gap.

Source: Lapierre, D., Braun, C. M. J., & Le Pailleur, L. (1992). A 54-Point Verbal-Performance IQ Discrepancy on the WISC-R: Cognitive Functioning of a Child from an Alternative School. Behavioural Neurology, 5(2), 97–106.

Interestingly, despite this massive change in cognitive profile, her full-scale IQ was virtually identical at both times (124 the first time, 122 the second time). This shows the incredible stability of the Wechsler full-scale IQ, even in the face of massive sub-test change. Probably because error in both directions cancels out when you have 10 diverse subtests.

The lesson is, whenever you see someone with a huge verbal-performance gap, it’s probably been exaggerated by error and the true gap is less extreme.