The purpose of this study was to examine the extent to which distinct patterns of fidelity of implementation emerged for 5,331 schools over a five-year course of implementing school-wide positive behavioral interventions and supports (SWPBIS). We used latent class analysis to classify schools based on their likelihood of implementing SWPBIS with fidelity each year, then assessed school and district predictors of classifications. A four-class solution fit the model well, with two patterns of sustained implementation (Sustainers and Slow Starters) and two patterns of practice abandonment (Late Abandoners and Rapid Abandoners). Significant predictors of group membership included grade levels served, enrollment, proportion of schools implementing SWPBIS in the district ("critical mass"), and size of the implementation cohort ("community of practice"). Elementary schools, larger schools, schools in districts with more schools already implementing SWPBIS, and those starting within a larger initial district cohort were more likely to be in the sustaining classes. Results are discussed in terms of understanding patterns of implementation in schools to enhance sustained implementation of school practices. [This article was published in "Prevention Science," v17 p992-1001 2016.]