The purpose of this study was to evaluate Achievement Mentoring, a school-based mentoring program designed to enhance high school student retention and achievement once identified as being at-risk for dropping out before graduation. We present findings from an individual-level randomized controlled trial that included 393 10th and 11th-grade students across three cohorts (2021-22, 2022-23, and 2023-24) from five Eastern states. Students were eligible for the program if they met one of three risk indicators in the prior year (ninth grade): missing 20 or more days of school, failing a core course, and/or incurring three or more disciplinary infractions. Outcomes used to assess impact included school attendance, credits earned, suspensions, and social and emotional outcomes (e.g., perceived support, self-efficacy, decision-making skills). We estimate program impact within an intent-to-treat (ITT) framework, regardless of their actual exposure to the AM intervention. The implementation study aimed to explore the extent to which the AM model was implemented as intended at each study site during the three implementation school years and the amount of programming students assigned to the AM condition received. Benchmark findings at the end of the first time point (10th grade) provide some promising support for the hypothesis that offering regular, individualized mentoring to students who meet one or more risk indicators at the start of 10th grade can improve their academic, behavioral, and social and emotional outcomes. Findings were less robust at the end of the second time point (11th grade), however, we document several limitations at this time point that suggest further research is warranted.