We investigate the effects of public school open enrolment, which allows students to enroll in any public school with available space, on fourth grade test scores. We find a small, positive effect on the average student; this benefit appears to stem from increased competition among schools, rather than directly through expanded choice opportunities. Among students whose catchment school is locally top-ranked according to test scores, greater choice is of no direct benefit; however, students whose catchment school is locally lowest-ranked earn higher scores when they have access to better local schools. Students in both groups benefit from increased school competition.