Research Findings: We evaluated the fidelity of implementation and the sustainability of effects of a research-based model for scaling up educational interventions. The model was implemented by 64 teachers in 26 schools in 2 distal city districts serving low-resource communities, with schools randomly assigned to condition. Practice or Policy: Although a logical expectation would be that, after the cessation of external support and professional development provided by the intervention, teachers would show a pattern of decreasing levels of fidelity, these teachers actually demonstrated increasing levels of fidelity, continuing to demonstrate high levels of sustained fidelity in their implementation of the underlying curriculum 2 years past exposure. Different profiles of variables predicted separate aspects of sustainability.