Student withdrawals were compared to course completers in two variants of a contingency-managed lecture (CML) course and a personalized instruction (PI) course. Within both CML sections, withdrawals performed 10-25% worse on unit quizzes and 20-30% worse on review exams than did peers who completed the course. Within PI, withdrawals had a retake frequency nearly four times higher, performed worse on review exams, and progressed at a slower rate than course completers. These results suggest that, regardless of teaching format, instructors should monitor student performance closely during the initial phases of a course, by the use of frequent quizzes in both CML and PI, so that appropriate intervention strategies can be arranged for students who are performing poorly academically, or at a low rate. (Author)