The three-tiered Positive Behavioral Interventions and Supports (PBIS) framework promotes the development of systems and data analysis to guide the selection and implementation of evidence-based practices across multiple tiers. The current study examined the effects of universal (tier 1) or school-wide PBIS (SW-PBIS) in one state's scale-up of this tier of the framework. Annual propensity score weights were generated to examine the longitudinal effects of SW-PBIS from 2006-07 through 2011-12. School-level archival and administrative data outcomes were examined using panel models with an autoregressive structure. The sample included 1,316 elementary, middle, and high schools. Elementary schools trained in SW-PBIS demonstrated statistically significantly lower suspensions during the fourth and fifth study years (i.e., small effect size) and higher reading and math proficiency rates during the first two study years as well as in one and two later years (i.e., small to large effect sizes), respectively. Secondary schools implementing SW-PBIS had statistically significantly lower suspensions and truancy rates during the second study year and higher reading and math proficiency rates during the second and third study years. These findings demonstrate medium effect sizes for all outcomes except suspensions. Given the widespread use of SW-PBIS across nearly 26,000 schools in the U.S., this study has important implications for educational practices and policies. [This paper was published in the "Journal of School Psychology" v73 p41-55 Apr 2019 (ISSN 0022-4405).]