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The Flynn effect is undoubtedly one of the most puzzling observations made during the last 30 years in the domain of human intelligence. In 1984, Flynn published an article in which he analyzed 73 U.S. studies (N total=7431) comparing the scores on several intelligence tests across time (Stanford-Binet Intelligence scales and Wechsler scales). All these studies compared the IQs obtained by a sample of individuals on each test and on the previous version of the same test, i.e., using norms collected in the U.S. population at two different points of time. These studies used 10 different norms, collected from 1932 to 1978. Several of Flynn’s questions are discussed in this chapter, bringing into focus the consequences of the FE on the clinical use of intelligence tests, especially the WISC-V.

Many Flynn effect (FE) studies compare scores across different editions of Wechsler’s IQ tests. When construct changes are introduced by the test developers in the new edition, however, the presumed generational effects are difficult to untangle from changes due to test content. To remove this confound, we use the same edition of Wechsler Intelligence Scale for Children–Fourth Edition (WISC-IV) across an 11-year period. Whereas previous research has reported the FE to be less than half the theoretical rate when comparing WISC-IV with Wechsler Intelligence Scale for Children–Fifth Edition (WISC-V), we find the rate of gain to be nearly identical to Flynn’s prediction when comparing only WISC-IV scores over the same time period. The FE is shown to vary significantly across the domains of cognitive ability, and thus changes to the construct coverage of the WISC-V Full Scale IQ (FSIQ) composite between editions significantly affect FE findings. Implications for future FE research are discussed.