Cognitive performance on “An Inventory of Piaget's Developmental Tasks” (IPDT) was related to the Scholastic Aptitude Tests and performance in both college chemistry lecture and laboratory classes. The IPDT is a valid and reliable 72-item, untimed, multiple-choice paper-and-pencil inventory. It has 18 subtests grouped into five problem areas representing different Piagetian tasks. Subjects (n = 225) from two different levels of introductory chemistry courses participated. IPDT scores were significantly correlated with SAT and placement data. In overall Piagetian development, “A” students rated higher than others. Performance in classification and proportional reasoning problem areas correlated with course achievement, particularly for higher-level students. Weakest areas of development were indicated by subtest scores and are described with implications for course performance. Finally, Piagetian tasks were related to learning and instructional activities in introductory chemistry classes and are discussed.