Does your cohort matter?

"To estimate peer effects in college achievement we exploit a unique dataset in which individuals have been exogenously assigned to peer groups of about 30 students with whom they are required to spend the majority of their time interacting. This feature enables us to estimate peer effects that are more comparable to changing the entire cohort of peers. Using this broad peer group, we find academic peer effects of much larger magnitude than found in previous studies that have measured peer effects among roommates alone. We find the peer effects persist at a diminishing rate into the sophomore, junior, and senior years, indicating social network peer effects may have long lasting effects on academic achievement. Our findings also suggest that peer effects may be working through study partnerships versus operating through establishment of a social norm of effort"--National Bureau of Economic Research web site.