The purpose of the study was to examine the extent to which the School-Wide Universal Behavior Sustainability Index: School Teams (SUBSIST; McIntosh, Doolittle, Vincent, Horner, & Ervin, 2009), a measure of school and district contextual factors that promote the sustainability of school practices, demonstrated measurement invariance across groups of schools that differed in length of time implementing school-wide Positive Behavioral Interventions and Supports (PBIS; Sugai & Horner, 2009), student ethnic composition, and student socioeconomic status (SES). School PBIS team members and district coaches representing 860 schools in 14 U.S. states completed the SUBSIST. Findings supported strong measurement invariance, for all items except 1, of a model with two school-level factors (School Priority and Team Use of Data) and 2 district-level factors (District Priority and Capacity Building) across groups of schools at initial implementation, institutionalization, and sustainability phases of PBIS implementation. Schools in the sustainability phase were rated significantly higher on School Priority and Team Use of Data than schools in initial implementation. Strong measurement invariance held across groups of schools that differed in student ethnicity and SES. The findings regarding measurement invariance are important for future longitudinal investigations of factors that may promote the sustained implementation of school practices.