The purpose of this study was to evaluate the stability and validity of a measure assessing sustainability of school-wide behavior interventions, the "School-Wide Universal Behavior Support Sustainability Index: School Teams" (SUBSIST). We assessed the stability of the SUBSIST across 3 years of measurement. We also assessed the convergent validity of two key SUBSIST factors, Team Use of Data and District Capacity Building, with more direct measures of these constructs. Results showed stability of the measure across multiple years and statistically significant correlations when compared with other external measures. Implications for research and practice are discussed.