This study aims to analyze the effects of a social-emotional learning program on the social-emotional competencies of high school students and their overall social, emotional, and psychological well-being. A total of 326 first-year students from a high school in G Province were assigned to an experimental group (n = 168) and a control group (n = 158). The eight-session program was conducted weekly over an eight-week period. Program effectiveness was examined using repeated-measures ANOVA on pre-, post-, and follow-up scores, analyzed with R 4.3.1 and SPSS 25.0. Results showed that the experimental group demonstrated significant improvements in social-emotional competencies and social, emotional, and psychological well-being compared to the control group, with significant group-by-time effects. These findings highlight the positive impact of SEL on adolescents and validate a developmentally grounded, structured SEL program applicable to classroom contexts, providing foundational evidence for SEL-based classroom practices and support systems.