We present quasi-experimental evidence of the impact of laptop use in college classrooms on academic performance. This study takes advantage of a college policy that requires all students to own a laptop computer, but allows individual teachers to require, allow, or ban laptops in their classrooms. Using student surveys, we find that students who are required to bring laptops to any of their classes on a certain day are significantly more likely to use laptops in laptop-optional classes than students who are not required to bring laptops to classes. Conversely, we find that students who are prohibited from bringing a laptop to at least one of their classes are significantly less likely to use laptops in their laptop-optional classes. We compare the grades of students who were and were not influenced to bring laptops to class by their course schedule and find consistent evidence of a negative impact of laptop use on student grades. Back-of-the-envelope calculations suggest that laptop use decreases course grades by between 0.14 and 0.37 grade points or 0.17 and 0.46 standard deviations.