In this paper, we report results from a multisite, student-level randomized controlled trial that examined the impact of the Building Assets, Reducing Risks (BARR) model on ninth-grade students. The BARR model is a comprehensive, strength-based approach that uses eight interlocking strategies to build intentional staff-to-staff, staff-to-student, and student-to-student relationships. This student-level RCT included approximately 4,000 ninth-grade students randomly assigned to treatment or control conditions in eleven schools. We examined six constructs of student experience including expectations and rigor, engagement, supportive relationships, social and emotional learning, sense of belonging, and grit; and five measures of academic success including course failure, core credits earned, grade point average, and Northwest Evaluation Association's (NWEA) Measures of Academic Progress (MAP) English Language Arts and Mathematics test scores. Findings suggest that BARR significantly increased core credits earned and mathematics achievement as measured by the NWEA MAP. Relative to the control group, BARR improved several aspects of student experiences in school, including an increased sense of supportive relationships and teacher expectations and rigor.