We report a randomized, wait-list controlled trial assessing the effects of school-wide positive behavior support (SWPBS). An effectiveness analysis was conducted with elementary schools in Hawaii and Illinois where training and technical assistance in SWPBS was provided by regular state personnel over a 3-year period. Results document that the training and technical assistance were functionally related to improved implementation of universal-level SWPBS practices. Improved use of SWPBS was functionally related to improvements in the perceived safety of the school setting and the proportion of third graders meeting or exceeding state reading assessment standards. Results also document that levels of office discipline referrals were comparatively low, but the absence of experimental control for this variable precludes inference about the impact of SWPBS. Implications for future research directions are offered. (Contains 3 tables.)