School safety is a pressing issue in urban schools. Yet, there is little research that shows why schools vary in safety and whether school practices mediate the influence of neighborhood characteristics. Using a unique dataset on Chicago Public Schools, this study examines the internal and external conditions associated with students’ and te achers’ reports of safety, showing that factors under the school’s control – their social and organizational structure – mediate the external influences of crime, poverty, and human resources in students’ residential communities. In particular, the quality of relationships between school staff, students and parents define safe schools in Chicago. In contrast, frequent use of suspensions is associated with less safe environments, even when comparing schools serving students with similar backgrounds. The findings from this paper point to the important role that school leaders and personnel can play in fostering safe school environments for students, even in schools that serve students from disadvantaged neighborhoods. Policymakers should attend to the important influence of supportive, collaborative relationships among teachers and parents, and between teachers and students, for mediating the adverse influences of neighborhood circumstances on student and teacher reports of safety.