The effectiveness of SEL programs in promoting students' social-emotional competencies is well documented in North American and European countries; however, evidence is more limited for other cultural and educational contexts. This dissertation examines the perceptions and experiences of teachers and students, cost of implementation, and effectiveness of the SEL program Fly Five in promoting children's social-emotional competencies in international schools in Morocco. The program consists of a comprehensive K-8 curriculum designed to explicitly teach five core SEL competencies - cooperation, assertiveness, responsibility, empathy, and self-control. Data collection took place during the 2022/23 school year in three international schools in Morocco, with 40 teachers in grades K-8 and approximately 450 students participating. The study used a pretest-posttest design with two schools receiving the program (treatment condition) and one school serving as the control (business-as-usual condition). Base- and endline data on children's SEL competencies and behavioral adjustment reported by students and teachers were collected in the fall and spring. Multi-level analyses revealed improvements in students' SEL competencies relative to students in the control group (ES = 0.40), which were driven by positive intervention effects on students' cooperation and empathy skills at one of the treatment sites. Interviews and focus groups indicated that student and teacher buy-in was high, especially in classrooms that used the program more consistently. While students liked that SEL classes were student-centered, teachers appreciated that the program was easy to use and encouraged students to get to know each other. Finally, the cost analysis revealed heterogeneity in program implementation and explored how costs varied by class size, number of teachers receiving training, and instructional time. This dissertation represents the first time Fly Five is being implemented and evaluated outside of the United States; thus, the study provided important, new insights into the successful implementation of the program abroad and guidance for future large-scale evaluations.