Charter schools have been growing in the United States and worldwide over the past two decades, and there is considerable interest in how they affect students remaining in traditional public schools (TPSs). Charter schools present important policy questions, as they often compete for the same students, educators, and resources as TPSs. On the one hand, increased competition from charter schools could lead to worse outcomes for students left behind if charter schools attract the best students and drain resources from TPSs. On the other hand, charter schools may provide positive alternatives for students who feel poorly matched to their default TPS and may stimulate competition that incentivizes all schools to improve their educational quality. Indeed, prior studies suggest that school principals respond to school competition by enacting curricular improvements and other changes.