“…Second, the policy I consider allows me to identify the effect of offering more (natural) science courses only, because it does not intervene on other subjects. Instead, changes in secondary school curricula usually imply a restructuring of many different courses and it is difficult to isolate the effect of one single subject [Altonji, 1995, Joensen and Nielsen, 2009, Gorlitz and Gravert, 2015, Jia, 2014. While my treatment also has multiple components, since taking advanced science also implies a change in classroom heterogeneity and composition, 8 I disentangle the curriculum from the peer channel, using an instrument for peers that exploits within-school variation over time in the ability of predicted peers, depending on whether the school offers advanced science or not.…”