Two instructional methods for a freshman physics course were compared: audio-tutorial (AT) instruction in a learning center and lecture-recitation-laboratory (LRL) instruction. Both random assignment and student preference were used to distribute the 575 students between the two methods. Course content, homework, and tests were identical. Achievement was evaluated by exam grades, adjusted for SAT math scores and math pretest scores. Questionnaires were used to gauge student attitudes toward the course. To determine long range effects of the rwo instructional methods, an analysis was made of the progress of the students, in terms of choice of physics classes, was designed to measure content and behavior under AT and LRL instruction, to show variations between the two methods, and to determine interrelationships among student achievement, student evaluation of teachers, and teacher behavior. Results indicated that AT and LRL lead to similar levels of achievement, but students with low math aptitude did better under AT while high math achievers did better under LRL. The observation instrument is included. (SL)