Education’s role as leverage for social mobility and for creating social positive externalities is crucial. However, little is known about the production function of university education, particularly in Greece, and how to make it more efficient. We construct a novel dataset from a top undergraduate economics department in Greece, by linking students’ personal characteristics and school performance with their university academic performance history. We then study the impact of the popular public policy in Greece of allowing students to transfer across departments based on social and financial criteria. Using various peer effects methodologies, we show that transferred students exert a significant negative externality across the quality spectrum on incumbent students.