The purpose of this study was to determine (1) whether the development of combinatorial schema as defined by Piaget is dependent on, or independent of, instruction, and (2) whether or not a prescribed treatment compatible with contemporary learning theories can develop the combinatorial operational abilities of students who are in a transitional period between concrete and formal patterns of thought. The study was limited to 61 sixth grade students taught by the investigator in a large mid-western city. Twenty-nine subjects in the experimental group received sequential science instruction to increase combinatorial skills of students, while the control group of 32 students received customary science instruction. Data were obtained from students scores on the Lorge-Thorndike Intelligence Test and from scores on a combinatorial pre-test and post-test developed by the investigator which contained both a verbal written answer portion and a manipulative portion. It was found that the combinatorial operational skills could be improved significantly by the experimental treatment. Verbal skills correlated significantly with intelligence; manipulative skills did not. (GR)