Background/Objectives: School-based universal mental health interventions offer an inclusive and scalable approach to promote mental health and well-being among children. This study evaluates the Let’s Learn About Emotions (Opitaan tunteista in Finnish) program, an evidence-based, teacher-led universal school-based intervention originally developed in Japan and culturally adapted for Finnish primary schools. 

Methods: A total of 512 fourth-grade students from 14 schools participated in the 12-week program during spring 2023. Using a mixed-methods design, we assessed (1) the program’s acceptability among students, parents, teachers, and school principals, (2) fidelity of implementation, and (3) changes in students’ mental well-being pre- to post-intervention. Quantitative data included standardized questionnaires with valid responses collected from 233 students at baseline and 209 students at post-intervention, as well as parents and teachers. Qualitative data were collected through focus group discussions involving parents, teachers, and school principals during spring 2024. 

Results: Acceptability was high across all respondent groups. Teachers adhered closely to the teaching manual, as confirmed by self-reports and direct classroom observations. Statistically significant improvements were observed in parent-reported conduct problems, hyperactivity, and peer problems, though student self-reports did not show similar benefits. 

Conclusions: The program was found to be both acceptable and culturally appropriate in the Finnish context. Findings from this study provide valuable insights for refining and improving the program for future implementation. To more rigorously examine its effectiveness, future studies should employ a randomized controlled trial design.