Schools are turning to research-based social emotional learning (SEL) practices to improve student achievement and school progress. Research to support SEL implementation, however, has lagged behind outcomes-based evaluations, often resulting in poor SEL program quality and fidelity. This mixed methods study explores SEL implementation at a high-needs high school to determine the extent the program’s implementation adhered to the identified model. The findings indicate the study school only minimally implemented the evidence-based model due to barriers also cited in peer-reviewed research and, therefore, the evidence-based program was not implemented as intended. This study validates the need for research to shift attention from efficacious outcomes-based studies toward establishing best implementation practices to ensure interventions are transferred and implemented with fidelity. Doing so should strengthen adherence to evidence-based models, improve the overall quality of SEL program implementation, and increase the likelihood of achieving the desired outcomes attributed to SEL program implementation. Impact Statement Currently the lack of evidence-based SEL implementation practices places schools interested in SEL at risk of poor program implementation in their unique settings. The findings in this study indicate there is a need to develop evidence-based SEL program implementation practices to support implementation in a context-specific manner that produces the desired outcomes, particularly in schools serving diverse student populations focused on closing race and income-based achievement gaps.