Tested was the hypothesis that science instruction based on task analysis will lead to the acquisition of the ability to perform certain Piaget volume tasks which have been characterized as requiring formal operations for their solutions. A Test on Formal Operations and a Learning Hierarchies Test were given to fourth- and sixth-grade students in a school which had used "Science - A Process Approach" and to fourth- and sixth-grade students in another school which had not used "Science - A Process Approach". After pretesting, students at each grade level at each school were divided by random assignment into experimental and control groups. The experimental groups received instruction based on learning hierarchies which incorporated ideas of Gagne; the control groups received instruction not related to hierarchies. All children were posttested with instruments used as the pretest. It was found that ability to perform the volume tasks at fourth-grade level may be related to experience in "Science - A Process Approach". A similar relationship with sixth-grade students was not found. A positive correlation was found between mental age and performance on the Test on Formal Operations. The results seem to support Piaget's theory of equilibration. (BR)