In this study, the authors examined students’ perceptions of their grades throughout an introductory biology course. Since large majorities of students prefer open-book exams (Moore and Jensen 2008); they sought to determine how these exams affect students’ perceptions regarding their eventual final grades. Although open-book exams may be useful in many courses, their data suggest that such exams often foster a false sense of confidence and a less accurate perception of final grades in courses such as the one described here. These results are consistent with an earlier report indicating that open-book exams may impede long-term learning (Moore and Jensen 2007), and call into question the long-term value of open-book tests in introductory science courses.