This study provides empirical evidence related to two critical assumptions in the student engagement literature in higher education--namely, the malleability of study effort and the causality of the relationship between study effort and student outcomes. We merged student-level administrative data on dormitory assignments, study effort in a hybrid course, and course performance from a regional college in China. Our results indicate that study efforts are more similar for a pair of randomly assigned roommates than for a pair of randomly assigned non-roommates, indicating the malleability of study effort. In addition, we provide evidence on the causal relationship between study effort and academic performance by using roommates' study efforts as an instrumental variable when estimating the effect of a student's study effort on course performance.