School-based mental health services (SBMH) may increase students’ access to care, which could yield benefits for mental health status and human capital-related outcomes. This paper uses a difference-in-differences design with 19 years of survey and administrative data to estimate the impacts of SBMH on a range of K-12 student outcomes. SBMH increases average outpatient mental health service use and reduces self-reported suicide attempts. There is weaker evidence that SBMH reduces suspensions and juvenile justice involvement, and no evidence that SBMH affects average attendance, standardized test scores, or self-reported substance use.