Schools are increasingly restricting cellphones worldwide amid concerns about achievement and mental health, yet causal evidence on school-level bans remains mixed. We examine cellphone restrictions in Chile before the pandemic, where teacher discretion over cellphone use generated classroom-level variation. Using administrative and survey data, we exploit cross-cohort, within-teacher, and within-student cross-subject variation in cellphone policies. Restrictions modestly reduce eighth graders’ in-class recreational cellphone use but not for tenth graders, suggesting uneven compliance. They also lower eighth graders’ perceived academic capability without affecting test scores. Our findings best extrapolate to decentralized policy contexts and contexts with uneven enforcement within schools.