Creating safe and supportive environments where students engage in prosocial behaviors is a priority and Positive Behavioral Interventions and Supports (PBIS) are used to achieve these goals. This study investigated relationships between PBIS fidelity, school climate, and office discipline referrals (ODRs). Participants were 204,701 students in 288 middle and high schools. Results indicated that additional years of PBIS implementation were related to greater fidelity, stronger school climate, and fewer ODRs. Findings also showed that students' perceptions of school climate in earlier years predicted fidelity and ODRs in later years. Further, ODRs reported during earlier years of PBIS implementation predicted fidelity and school climate in later years. Implications for research and practice are discussed, including considerations for how the whole-school environment can affect PBIS implementation. Future research should investigate school level (i.e., elementary, middle, and high school) and school diversity as moderators of the relationship between PBIS fidelity, school climate, and behavioral outcomes. Researchers and policymakers should use multidimensional school climate scales rather than relying only on unidimensional measures. Finally, since school climate influenced fidelity, schools that create safe/supportive environments can maximize the effective implementation of complex strategies like PBIS.