Introduction: This paper presents an assessment of the impact of a social and emotional competencies development program, based on the SEA theoretical model (attention to and understanding emotions, emotional regulation and repair, and adaptive social expression of emotions), in adolescents and preadolescents. Method: Students' homeroom teachers implemented the program in a public secondary school over one school year. The participants of this study were 156 young people from ages 11 to 14 years old, all of them students in the first year of the Spanish secondary education system. A quasi-experimental design, with pre/post-test measurements and a control group, was used to evaluate program effectiveness. The tests used for this assessment measured variables of participants' social-emotional competencies, empathy and social adjustment. In addition, a follow-up assessment was carried out 3 months after the end of program implementation. Results: The study demonstrates a significant improvement in the social-emotional competencies of program participants, especially in the competencies most related to adaptive social expression of emotions. There were also significant improvements in empathy and social adjustment. Discussion and conclusions: The possibility of enhancing social-emotional competencies through the application of a direct classroom intervention program during one school year was confirmed, and the SEA program becomes a candidate to achieve this goal.