This study investigated the developmental relationships between a battery of cognitive tasks--including Piagetian operations of conservation, classification, and seriation--and early reading achievement. Subjects were 128 kindergarten through third-grade students at a suburban elementary school. They were administered a battery of cognitive tests and reading achievement measures. Results were analyzed using t-tests of the differences between group means, one-way analysis of variance, Pearson correlation coefficients, and multiple regression analysis. The major findings of this study were that standardized psychometric measures were more related to reading achievement than were the Piagetian tasks, although conservation was a significant predictor of achievement at the kindergarten and first-grade levels. There were also developmental differences in the relationships of all variables to reading achievement. In the first-grade sample, it appears that the instability of cognitive thought represented by the transitional phase of conservation may interfere with academic achievement. (Author/TS)