Positive behavioral interventions and support (PBIS) is a multitiered framework for behavioral support that is being increasingly implemented in schools. Although research has linked PBIS to improved student outcomes, less research is longitudinal and considers both academic and behavioral outcomes. This study examined the relationships between changes in school-wide (i.e., Tier I) PBIS implementation level and changes in disciplinary and achievement outcomes over a 2-year period. Participants included 85 Ohio schools with data on PBIS implementation fidelity (from the tiered fidelity inventory, or TFI), out-of-school suspensions (OSSs), and statewide achievement tests for the 2015-2016 and 2016-2017 school years. Linear regressions were conducted to examine the degree to which changes in TFI Tier I scores predicted changes in OSS and achievement scores when controlling for school-level demographic variables that also were related to the outcome variables. Changes in TFI Tier I scores was found to significantly predict changes in OSS per 100 students but not changes in achievement scores.