Intelligence and Achievement: Just how Correlated are they?

The purpose of this study was to summarize the correlations between individually administered tests of intelligence and achievement reported in various test manuals and published journal articles. An exhaustive review of published findings yielded data that were organized into two groups: studies involving correlations between (a) IQ and achievement test composites and (b) IQ and achievement subtests. Within these two areas, data were further divided into studies involving small (n 200) samples. For the large studies, the ability/achievement composite correlations for the K-ABC (.74) followed by the CAS and WJ-III (both .70) were the top ranked. Results for the large-scale ability and achievement subtest studies demonstrated that the CAS (Standard and Basic Batteries, respectively) had the highest correlations with achievement subtests (.65 and.64), followed by the K-ABC (.63). Thus, the two measures of cognitive processing consistently had the highest correlations with achievement despite the fact that they do not contain achievement-like subtests found in all the other ability measures. These and other findings are discussed and contribute to the conclusion that measures of basic psychological processes offer a viable alternative to traditional IQ for the correlation with achievement.