Groups of 139 and 137 undergraduate students took three physics courses taught by either the personalized system of instruction or the lecture-discussion method. Students from these groups were compared in two subsequent chemistry courses and a subsequent biology course. The PSI group achieved significantly higher grades in each case. The junior year major area grades of students who majored in applied mechanics 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 selective attrition had occurred. Groups of 139 and 137 undergraduate students took three physics courses taught by either the personalized system of instruction or the lecture-discussion method. Students from these groups were compared in two subsequent chemistry courses and a subsequent biology course. The PSI group achieved significantly higher grades in each case. The junior year major area grades of students who majored in applied mechanics 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 selective attrition had occurred.