In this paper we study the effect of opening a new high school on pupils’ schooling at the end of lower secondary education. We use high school openings to highlight the constraint local school supply exerts on individual schooling decisions. Our working sample covers all pupils enrolled in 9th grade between the school year 2007-2008 and the school year 2010-2011 in France. Our estimation strategy (a generalized difference in differences) takes advantage of the variation in time and space of the openings of high schools to estimate the causal effect of an increase in school supply on the allocation of pupils at the end of 9th grade. We show that opening a new high school significantly increases the probability for pupils from neighboring middle schools to continue in higher secondary education. This increase is due to a larger proportion of pupils going to the vocational track. Furthermore, the effect is mainly driven by low achieving students. Joint with Meryam Zaiem (Dares).