The development of evidence-based interventions (EBIs) for the prevention of behavioral health problems is well supported. However, limited data exist on the sustainability of EBIs once initial support has ceased. The current study assessed, at 2 years after initial start-up support: (1) What percent of schools sustained EBI implementation? (2) To what degree did sustaining schools implement the EBI with fidelity? (3) What were the primary reasons for not sustaining the EBI? (4) What theoretical and contextual factors during initial start-up support predicted sustainment of the EBI? The study used process evaluation data from the dissemination of the Botvin "LifeSkills Training" (LST) middle school program in 158 school districts (including 419 schools). Fifty-one percent of districts sustained the EBI and most of these sustaining districts reported following key fidelity guidelines. Primary reasons for discontinuing centered around low teacher or administrative support and turnover. Significant predictors of sustaining LST were higher ratings of LST's complexity, benefit, and compatibility by teachers; more positive perceptions of organizational support from administrators; and smaller proportions of Black students. Results show that EBI sustainment and fidelity of implementation post-initial startup support are feasible, though likely not for all schools. Findings also suggest that cultivating support for the EBI among staff during start-up support may be helpful for sustainment and that social determinants of a school have a complex relationship with EBI sustainment. Future research should explore true causes of differences due to race/ethnicity as well as COVID-19 effects.