BackgroundThe development of social competencies is key for enhancing both cognitive and non-cognitive skills among students. These competencies are central to students' ability to function socially, feel included, and experience overall well-being within the school environment. Schools can play an active role in promoting and shaping these outcomes by implementing various strategies. This study presents and reports on the outcomes of a six-week social-emotional intervention program implemented by class teachers. MethodsThe pilot study employed a two-arm cluster non-randomized trial with a pretest-post-test design. The study evaluates students' social competencies as the primary outcome and social functioning, social inclusion, and school well-being as the secondary outcomes. Students in the intervention group participated in a six-week social-emotional learning intervention, attending two sessions each week, while the control classes followed the regular curriculum. ResultsData were collected from both teachers and students. Student-reported data were collected from 266 students (n = 124 girls, n = 142 boys) aged 8 to 14 (M = 9.84) and from teachers on 212 students (n = 92 girls; n = 115 boys). Results of the linear mixed model analysis showed for teacher reporting on students’ outcomes a decrease in internalizing (β = -0.85, p = 0.035) and externalizing behavior problems for students in intervention classes (β = -6.84, p = 0.020). No significant changes were observed in social-emotional competencies, social inclusion and school well-being. ConclusionAfter the social-emotional intervention program reduced internalizing and externalizing behavior problems were observed, with age moderating both outcomes. The results are consistent with previous research; however, they also suggest that the intervention could benefit from adjustments, such as a longer implementation period and follow-up evaluation. External factors such as the COVID-19 pandemic and repeated school closures at the time of the study may have impacted the results additionally.