<p>Early childhood educators play a central role in supporting children’s social-emotional development, yet many reported high stress and limited access to structured professional learning. This study evaluated the BEST YO program, an 18-hour social and emotional learning (SEL) professional development course designed to support teachers’ social-emotional competence (SEC) and well-being. A quasi-experimental pretest–posttest design was conducted with 71 early childhood educators in Taiwan assigned to in-person, synchronous online, or waitlist control conditions. Quantitative outcome measures were supplemented by open-ended responses and teacher interviews to provide contextual understanding of program experiences and perceived relevance, application, and impact. Participation was associated with significant improvements in teachers’ SEC across both delivery formats. Changes in well-being varied by format, with increases in emotional well-being and self-compassion and reductions in emotional exhaustion primarily observed in the in-person condition. No short-term changes were detected in work performance indicators. Teachers’ reflections described increased emotional awareness, intentional pausing in challenging situations, and changes in professional interactions. The pattern of findings suggested that SEL-oriented professional development may influence teachers’ internal regulatory capacities before observable changes in teaching practice emerge. These results highlighted the importance of supporting teachers’ own social-emotional development as part of sustainable SEL implementation in early childhood education.</p>