Schools play a key role in child and youth development as both social microcosms of the broader society and reciprocally influencing people and communities. As such, schools can function as a protective factor that promotes safety, motivation, relationships, and support for positive student outcomes. However, schools may also function as a risk factor with inflexible bureaucratic structures that employ harsh and exclusionary discipline that contributes to negative outcomes. This chapter discusses schools as a social institution by examining the student­, teacher­, and building-­level predictors of academic and social and emotional success, as well as schools as a locus for preventive interventions. [This chapter was published in Z. Sloboda, H. Petras (Eds.), "Defining Prevention Science. Part II," ISBN 978-1-4899-7423-5, p151-169. This book is part of the series, "Advances in Prevention Science."]