<p>Interventions to improve student–teacher relationships hold promise for improving the social–emotional climate of the classroom and students’ social–emotional well-being. However, if not successfully implemented, these interventions are unlikely to have their intended impacts on teacher practices and student outcomes. In the current paper, we conduct a case study mixed methods examination of implementation determinants and outcomes of the Equity-Explicit Establish-Maintain-Restore (E-EMR) program. E-EMR is a student-teacher relationship intervention in which teachers are trained to integrate bias-reduction strategies into practices for improving relationships. Data for this study came from interviews and surveys with teachers (n_surveys = 43; n_interviews = 15) and administrators (n_surveys = 3) within three schools that were randomized into the intervention condition of a pilot randomized control trial of E-EMR. All three schools demonstrated moderate levels of teacher-reported fidelity, but only one school indicated strong likelihood of sustainment into the next school year. Higher levels of fidelity appeared to be the byproduct of active implementation supports combined with individual-level and innovation-specific facilitators. However, organizational factors within the inner setting were particularly salient determinants that likely enable or obstruct the sustainment of an effective program. This study provides insight regarding determinants that can support program implementation as well as methodology that can be employed to examine implementation research questions for social–emotional programs in school settings.</p>