The study concerned (1) identifying component processes of discovery and rule learning; (2) describing differences in learning outcomes produced by the two instructional methods, and; (3) optimizing learning. It was believed that understanding the effects of aptitude, instructional methods, and their interaction is important in the study of learning and problem solving. Two experiments were performed to investigate the effects of aptitude and instructional methods on learning concepts of probability. The two methods were learning by discovery and learning by rule versions of programmed instruction. Results supported the hypothesis that the outcome of discovery is the structural integration of previously known concepts, while the outcome of rule learning is the addition, subject scoring low on tests of relevant abilities performed better by every measure when instructed by the rule method. The data indicates that the result of learning by discovery is a well integrated cognitive structure because subjects can solve problems that require relating principles previously learned. (BW)