Between Merit and Chance - Social Inequality and School Choice in Mexico City's Upper Secondary Education Admissions Reform

In 2025, the admission system for public upper secondary education in Mexico City was reformed, intending to end the use of the standardized test used to assign students to schools and replace it with a lottery. However, because the most selective high schools decided to keep the exam, the reform resulted in a two-track system: a test for the most selective ones and a lottery for the rest. This increased the differences in applying to each segment of schools in a context already marked by institutional heterogeneity and social segmentation in access to selective schools. While the reform aimed to increase equality of opportunity in the transition to upper secondary schooling, increased institutional heterogeneity changed the conditions under which applicants choose schools, leading them towards diverging decisions depending on their socioeconomic and educational backgrounds. Using rich administrative data and logistic regression, this thesis analyses how this reform affected the relationship between an applicant’s social origins and educational characteristics and their decision to apply to the schools that require an exam. It finds that under the new system, the share of applicants choosing exam schools decreased from 78.7% to 59.4%. This drop was associated with a strengthening of the link between applicants' social origins and educational characteristics and their choice of exam requirement schools, as these variables became stronger predictors in the new system. These findings highlight the difficulty of isolating the admissions reform, in its pursuit of equality of opportunity, from the broader inequalities it operates within. They also show how the design of educational systems interacts with social inequality, pointing to school heterogeneity and the dynamics that result in differences in students' social and educational characteristics as necessary targets for increasing equality of opportunity in the transition to upper secondary schooling.