This data set consists of three studies designed to explore the substance and method of cognitive learning about scientific facts and theories within a cognitive developmental framework. Study I was designed to assess children's understanding of four science concepts (electromagnetism, gravity/falling objects, chemical bonding, and biology) at different points along the age/experience continuum. The child was asked to predict the results of an experiment and explain the reasons for his/her prediction. After the experiment was conducted, the child was asked to describe and explain the results. The subjects, five boys and five girls, were selected by their teachers from the first, third, fifth, seventh, and ninth grades, representing a range from average to bright in science-related activities. Study II aimed to assess the consistency of levels of scientific understanding and the relationship between developing science concepts and logical reasoning skills. In addition to the electromagnetism and gravity interviews, children were given a measure of class inclusion (Inhelder & Piaget, 1969) and a measure of substance and weight conservation (Inhelder & Piaget, 1958). Participants were 15 preschoolers, 30 kindergartners and 60 first graders. Study III examined developmental patterns in how children progress in science understanding. Participants received a battery of pretests and posttests including concrete operational tasks, a formal operational task, and two science problem interviews. Three groups of 10 students in the first, third, and fifth grades took part in an experimental 12-session extracurricular science enrichment program. Similar control groups at each of these grades were selected from the same volunteer pool. Each experimental child also received a series of debriefing interviews immediately following each laboratory session probing the child's understanding of the energy experiment presented. The Murray Center holds transcripts of science problem interviews from Studies I and II, and transcripts of the Study III debriefing sessions. The Murray Center also has machine-readable data from the logical reasoning measures and the scored levels of development from the science problem interviews.