We used a cluster-randomized controlled trial to examine the impacts of a technology- and game-based social-emotional program, the "Adventures Aboard the S.S. GRIN" ("Adventures"), on students' social skills development. Eighty-eight third-grade classrooms (N = 1645 third-grade students) across four California public school districts were randomized to treatment or control. Analysis of student demographic data indicated that 49% were male, 51% were female, approximately one-third were Latinx, and about 50% qualified for free and reduced lunch. Two-level hierarchical linear model analysis results indicated that "Adventures" had significant and meaningful impacts on students' social-emotional learning (SEL) skills. The findings of Adventures shine new lights on a growing effort to support all students, including those identified by their teachers as having social-emotional challenges. It also expands our knowledge about the potential role of technology in addressing SEL competencies.