Since the COVID-19 pandemic, mental health challenges among children and adolescents in South Korea have intensified with rising rates of depression and suicide. Proactive interventions focusing on mental well-being are needed to address this critical issue. This study examines the effectiveness of the Mindfulness-based Social-Emotional Growth (MSEG) program for enhancing the mental health of elementary school students in Korea. This quasi-experimental study evaluated the impact of the MSEG program on students at an elementary school in Gyeonggi-do, South Korea. A total of 70 students (35 from lower grades [grades 1-3] and 35 from upper grades [grades 4-6]) participated in the 12-week intervention group, while 72 students were in the control group. Pre- and post-intervention assessments measured social-emotional, mindfulness, and clinical domains. The findings revealed significant improvements in emotional regulation across all grades. Lower-grade students showed substantially reduced anxiety and depression, while upper-grade students demonstrated enhanced resilience compared to the control group. These results indicate the potential of the MSEG program to promote early mental health when integrated into elementary school curricula. Further research is needed to adapt the program to diverse educational settings and optimize its effectiveness and impact.