This study investigated the long term effects of the Personalized System of Instruction (PSI) method at the University of California, San Diego. Groups of 139 and 137 undergraduate students took three physics courses taught by either the PSI method or the lecture/discussion method. Students from these groups were compared in two subsequent chemistry courses and a subsequent biology course. The chemistry and biology courses were taught using lectures and discussion sections. The PSI group achieved significantly higher grades in both the physics courses and the subsequent courses. The fact that the PSI students achieved higher grades in the subsequent lecture courses seems to indicate that they were not at a disadvantaged because of the earlier PSI courses. The junior year major area grades of students who majored in applied mathematics and engineering sciences, biology, chemistry, and physics were also compared. In each case, the PSI group achieved significantly higher grades. For each comparison, the mean high school grade point average, SAT scores, and freshman university grade point average were used to verify that no selected attrition had occurred. (Author/RC)