Commuting to educational opportunity? School choice effects of mass transit expansion in Mexico City

School choice policies aim to increase educational access by weakening the link between a student's residence and his choice set, but long commutes and other barriers may constrain families from selecting otherwise desirable schools. Leveraging a mass transit expansion in Mexico City's suburbs as a natural experiment, we find that a new train raised demand for elite and more distant schools, but only among high-achieving students with highly-educated parents. These students were also more likely to be assigned to elite and more distant schools under the test-based assignment mechanism. In contrast, we find little effect on the choices or assignments of low-achievers or those with lower-education parents. These results highlight the complementarities between transit access and school choice as well as the potential limitations of choice policies in large urban areas.