Student-teacher relationships are important to student outcomes and may be especially pivotal at the high school transition and for minoritized racial/ethnic groups. Although interventions exist to improve student-teacher relationships, none have been shown to be effective among high school students or in narrowing racial/ethnic disparities in student outcomes. This study was conducted to examine the effects of an equity-explicit student-teacher relationship intervention (Equity-Explicit Establish Maintain Restore, or E-EMR) for high school teachers and students. A cluster-randomized pilot trial was conducted with 94 ninth grade teachers and 417 ninth grade students in six high schools. Teachers in three schools were randomized to receive E-EMR training and follow-up supports for one year. Teachers in three control schools conducted business as usual. Student-teacher relationships, sense of school belonging, academic motivation, and academic engagement were collected via student self-report in September and January of their ninth-grade year. Longitudinal models revealed non-significant main effects of E-EMR. However, there were targeted benefits for students who started with low scores at baseline, for Asian, Latinx, multicultural, and (to a lesser extent) Black students. We also found some unexpected effects, where high-performing and/or advantaged groups in the E-EMR condition had less favorable outcomes at post, compared to those in the control group, which may be a result of the equity-explicit focus of E-EMR. Implications and directions for future research are discussed.