We study the effects of introducing school-based mental health services (SBMH) in K-12 schools on a range of outcomes, including students’ mental health, mental health services use, educational outcomes, and criminal-justice outcomes. Mental health problems are common among children and adolescents. A substantial body of evidence suggests that poor mental health is a strong predictor of student’s lower academic achievements, school attendance, and disruptive behavior. Mental health problems in youth can also have negative consequences across the entire life course, affecting educational attainment, social adjustment, and economic wellbeing. Early identification and treatment of mental health problems in childhood and adolescence may therefore be especially valuable, but less than half of children with mental health problems receive professional help. A variety of economic, social, psychological barriers prevent youths from accessing appropriate mental health services. Schools are a promising space to look for solutions to these problems, since youth spend so much of their time in educational settings. However, we lack rigorous evidence on the effects of large-scale implementation of robust school-based mental health services. To generate new evidence, we will use a generalized difference-in-differences design focusing on the staggered roll out of school-based mental health services across schools in Hennepin County, Minnesota that uses panels of individual student health, health services use, academic, and criminal justice outcomes.