Peer Effects in Math and Science

This paper examines how skills are shaped by social interactions in schools and families. We focus on critical course choices in high school and naturally occurring peer groups. We overcome the identification challenges of estimating peer effects in education by exploiting exogenous variation in choice sets. First, we analyze a universal free-choice reform causing a fall in math-science skills. We show how it amplified the falling skill supply in peer groups with a stronger math-science norm, particularly for boys. Second, the detailed nature of our administrative data allows us to analyze the underlying mechanisms. We exploit quasi-experimental variation stemming from a pre-reform pilot scheme. The pilot induced a random subset of older siblings to choose advanced math-science at a lower cost, while not directly affecting the course choices of younger siblings. Therefore, any influences of the pilot on the younger siblings may be attributed to the peer influence of the older sibling. We find that younger siblings are 2-3 percentage points more likely to choose math-science if their older sibling unexpectedly could choose math-science at a lower cost. Spillovers are strongest among closely spaced siblings, in particular brothers. We argue that competition is likely the driving force behind younger siblings conforming to their older siblings’ choices. JEL Classification: I21, I24, J24, J16, J12, Z13.