A safe environment is a prerequisite for productive learning. This paper represents the first large-scale analysis of how feelings of safety at school affect educational outcomes. Using a unique longitudinal dataset of survey responses from New York City middle school students, the paper provides insight into the causal relationship between feelings of safety and academic achievement. The survey data include the reported feelings of safety for more than 340,000 students annually from 2007-2010 in over 700 middle schools. Findings show consistent negative effects of feeling unsafe on test scores. The paper explores the mechanisms through which feeling unsafe in the classroom may impact test scores, and multiple robustness checks support the validity of the causal claim.