What drives segregation? Evidence from social interactions among students

We study the dynamics of group formation using data on the online social networks of a cohort of undergrad-uate students. We document gradual endogenous segregation along the ability dimension. We show that "high ability"students interact more and more with high ability students over time (active segregation). Instead, "low ability"students "reach out"to high ability students but are not reciprocated (passive segregation). Exploiting our administrative records on student performance we provide evidence that information about ability is an additional driver of social interactions in educational settings, besides the homophily hypothesis