Time Varying Effects of Elite Schools: Evidence from Mexico City

We study whether the academic effects of being marginally admitted to an elite science school depend on the admission year as a reflection of how school characteristics change over time. We take advantage of five years (2005-2009) of administrative data on a large centralized high school admission system. We find that the effect on mathematics test scores at the end of high school decreases each year, starting positive and statistically significant in 2005 and ending not significant by 2009. We show that the discontinuous jumps in peer quality and other school characteristics induced by elite school admission have not systematically changed. However, the gains in school quality decreased, affecting the treatment definition. Varying relative school quality limits the external validity of otherwise internally valid estimates.