Selective school admissions and student achievement: Evidence from a policy reform in Chile

Whether selective school admissions generate genuine academic value added or whether observed achievement differences primarily reflect student selection remains contested. This paper examines this question using a nationwide reform in Chile that substantially restricted selective admissions to Bicentennial secondary schools after 2016. The reform provides an opportunity to compare cohorts admitted before and after selection was curtailed. I draw on linked administrative enrolment records and national achievement data (SIMCE) covering six student cohorts, three admitted before the reform and three after it, and estimate a pooled difference-in-differences model interacting Bicentennial status with a post-reform indicator, conditioning on prior Year 4 achievement and socioeconomic background. The main results are robust to school fixed effects, to corrections for non-random attrition, and to multilevel specifications. Before the reform, Bicentennial Schools enrolled more socioeconomically advantaged and higher-achieving students and displayed sizeable achievement gaps relative to other schools. Following the reform, the socioeconomic and academic composition of their student intake moved markedly closer to the system average. Consistent with this convergence, the estimated achievement advantage associated with attending a selective school declines sharply in the post-reform cohorts. Prior to the reform, the Bicentennial advantage was about 0.28 SD in reading and 0.39 SD in mathematics; as selection was restricted, it attenuated by roughly 0.15 SD in reading and 0.18 SD in mathematics. The residual post-reform advantage is concentrated in the one channel through which these schools can still select on academic grounds. Overall, the findings suggest that much of the previously observed performance advantage of selective schools reflected student sorting rather than superior instructional effectiveness.