In this study, the authors investigated the role of overconfidence on students' performance on multiple-choice examinations. The authors examined the difference between students' self-assessed probability of selecting each correct answer and the proportion of correct answers that they actually selected. Results show that high-performing students discriminated better between difficult and easy multiple-choice questions than did low-performing students. Poorer students exhibited significant overconfidence with difficult questions. Generally, students displayed underconfidence with easy questions and performed better on multiple-choice questions when they were asked to provide reasons contradicting their choices. These results suggest that students can be trained to perform better on standard multiple-choice exams through preparation involving their providing reasons contradicting their choice of answers. (Contains 4 tables.)