This paper examines the competitive effects of a unique school choice program implemented in the late 1990s, Wisconsin's open enrollment program, which allows families to send their children to schools outside their home district. In contrast to other school choice programs, districts not only face negative consequences from losing students and state funding, but they also stand to gain in the event of student emigration from other districts. The identification approach exploits differences in the number of schools in bordering districts, which affects inter-district ease-of-transfer. Estimates produce three main conclusions. First, districts that experience student out-migration produce higher standardized test scores in the subsequent year. Second, these effects are most evident among districts for which out-migration, expressed as a percentage of enrollment, falls in the upper quartile of all districts under consideration. Third, districts do not appear to respond to in-migration, indicating that districts place more emphasis on (and have more control over) preventing out-migration, as opposed to encouraging in-migration. These findings provide evidence that schools respond to competitive forces by improving quality. (Contains 13 tables.)