Early adolescence and the transition to middle school bring about many challenges for students and negative outcomes are not uncommon, including academic decline and social maladjustment. This developmental period is also marked by increased risk of mental health-related difficulties. Strengthening students' social and emotional competencies through the delivery of school-based Social and Emotional Learning (SEL) programs has been suggested as one strategy for promoting positive development and preventing negative outcomes. In particular, the delivery of developmentally appropriate and evidence-based SEL programs at the universal level of tiered supports has the potential to benefit many students. The current study presents findings from a randomized controlled trial of the Speaking to the Potential, Ability, and Resilience Inside Every Kid (SPARK) Pre-Teen Mentoring Curriculum for 357 students from two schools. Results revealed that students who received the curriculum showed significant improvements in knowledge of curriculum content and principles; communication, decision-making, and problem-solving skills; emotional regulation; and resilience compared to students in the comparison condition. Results provide initial evidence for the efficacy of the SPARK Pre-Teen Mentoring Curriculum for middle school students. Study strengths and limitations as well as directions for future research and program development are discussed.