The relationship between Piagetian and school achievement tests was examined through a meta-analysis of correlational data between tests in these domains. Highlighted is the extent to which performance on Piagetian tasks was related to achievement in these areas. The average age for the subjects used in the analysis was 88 months, the average IQ was 107. Mathematics and reading tests were administered. Averaged correlations indicated that Piagetian tests account for approximately 29% of variance in mathematics achievement and 16% of variance in reading achievement. Piagetian tests were more highly correlated with achievement than with intelligence tests. One implication might be the use of Piagetian tests as a diagnostic aid for children experiencing difficulties in mathematics or reading. (Author/GK)