What is behind class attendance in college economics courses?

How class attendance influences students' performance remains unclear. Specifically, do students learn more <italic>in class</italic> if they attend more classes, or does class attendance create incentives for students to study harder <italic>outside class</italic>? To better understand this relationship, we designed an attendance policy in an economics course that does not significantly change students' attendance rates. Students who scored below a cut-off on the midterm exam were required to attend subsequent class lectures even though attendance had been implicitly made mandatory for all students, accounting for 10% of the course grade. Our regression discontinuity analysis suggests that our attendance policy significantly improved students' performance on the final exam, even though it had minimal impacts on their attendance rates. We also found that the policy worked via inducing students to reallocate their time spent studying other courses <italic>outside class</italic> to economics.