This paper explores the incentives that students and instructors face when a new technology that grants access to online class materials is introduced. We examine the consequences for attendance and for the composition of live lectures. We also analyze how various sources of heterogeneity in students' characteristics, learning styles, and technologies affect individual incentives to attend lectures when different degrees of access to online resources are available. In particular, we consider heterogeneity in the outside options of students and the effectiveness of different online materials. We obtain some testable implications that may guide empirical researchers towards estimation strategies that better capture how granting access to online class materials impacts attendance and class composition.