A flipped classroom provides students with course content in the form of videos, readings, and/or simulations that they complete during the time traditionally used for homework assignments while in-class time is devoted to hands-on group learning activities. Project BoxSand is gathering quantitative data on how students in a flipped classroom, algebra-based introductory Physics series, interact with the course website and other online components or materials. Using educational data mining methods, I analyzed student use of the Mastering Physics by Pearson website used for homework submission, and the impact on exam performance. I found a positive correlation between the completion of the Post-lecture Mastering Physics assignments by the due date and exam performance. Students completing Post-lecture Mastering Physics assignments by the due date tended to perform better on exams than students who either didn't complete the assignments or completed them after the due date.