Seventeen medical school students who participated in a commercial test preparation course were matched with 17 other students judged to be of equal ability. These two groups were compared on the basis of their scores on Part I of the National Board of Medical Examiners (NBME). The two groups were matched closely on both the grade point average for the first two years of medical school and scores on a pretest. Students who took the commercial course scored significantly higher on Part I and 16 of the 17 passed, whereas 9 of the control group failed. Questionnaire and interview results indicated that: (1) students were motivated to take the course by fear of failure on the examination; (2) the course offered a well organized approach to condensing two years of study and concentrated on information relevant to the examination; and (3) that instruction in test-taking techniques was not among the most valuable features of the course. (CTM)