U.S. public school students increasingly attend schools with sworn law enforcement officers present. Yet, little is known about how these school resource officers (SROs) affect school environments or student outcomes. Our study uses a fuzzy regression discontinuity (RD) design with national school-level data from 2014 to 2018 to estimate the impacts of SRO placement. We construct this discontinuity based on the application scores of nearby police agencies for federal school-based policing grants. We find that SROs do effectively reduce some forms of violence in schools, but do not prevent school shootings or gun-related incidents. We also find that SROs intensify the use of suspensions, expulsions, police referrals, and arrests of students. These effects are consistently over two times larger for Black students than White students. Finally, we observe that SROs increase chronic absenteeism, particularly for students with disabilities.