Students enter college exceedingly confident that they will earn high grades and engage themselves fully in their courses. However, students' grades and academic behaviors often do not match their expectations. This is especially true in introductory science courses, where grades and academic engagement are often low, even in courses taught by award-winning instructors. In this study, the authors attempt to understand what underlies students' academic behaviors and overconfidence. To do this, they analyze the grades, academic behaviors, and academic predictions of students who earned differing final grades in a large introductory biology course. The study included 278 students enrolled in an introductory "mixed-majors" biology course at the University of Minnesota. The study shows that first-year students are exceedingly confident of their abilities to succeed in introductory biology courses, despite the fact that these students have a six-year graduation rate of only 29-33% (Jensen & Moore, 2008). In this study, the authors extended that work by characterizing how students' academic perceptions throughout the semester and students' behaviors correlate to their earned grades. Data presented here indicate that students who earn differing final grades in an introductory biology course display different academic behaviors throughout a semester, and, after the first exam, have dramatically different perceptions of their final grades. (Contains 2 figures and 2 tables.)