Introduction: The global trend of new curricula in many OECD countries indicates that social interaction skills are becoming increasingly important. Educators need to start fostering the development of learners' social competences, which requires development of their own knowledge and skills. This study investigated the possible change in teachers' knowledge, their applied knowledge, and their sense of competence during the Lions Quest (LQ) workshops. For us to measure this, the participants responded to the LQ inquiry. Method: We collected ten samples from 2120 participants in nine countries. Of all the participants, 1206 teachers attended the LQ teacher workshops (intervention group). Comparison data were collected from 914 teachers not participating in the LQ, and the mean sum scores from the multi-item measures were computed and used as variables in further analyses. We specified a multivariate mixed design, in which we examined the effect of the intervention with regard to mean change over time across groups in the variables. Sample-wise, we explored the within-group mean differences between pre- and post-test scores and evaluated the effect sizes for the intervention. Results: The results indicated that the intervention had a positive effect on the participants across all samples apart from one, and that teachers benefitted from continuous training on social and emotional learning (SEL). Discussion and Conclusion: The results of the present study indicate that even a relatively short-term, low-cost intervention in teachers' SEL is worthwhile. Successful SEL enables teachers and their students to face challenges more easily, inside and outside school, now and in the future.