This study examined the effects of an evidence-based social and emotional learning (SEL) program, The RULER Approach to Social and Emotional Learning (RULER), on teacher self reports of engagement, teacher-student interactions, and burnout. Participants were 47 teachers from 19 public schools in Spain who either volunteered for training on RULER (n = 24) or eLearning (n = 23). Multivariate Analysis of Covariance (MANCOVA) was conducted separately for each outcome. Teachers in the RULER as compared to eLearning group had significantly higher scores on many outcomes even after controlling for gender, age, trait affect, and personality, as well as pre-test scores on all outcomes. These findings extend the literature on the effectiveness of SEL programs for the improvement of teacher practices; they also advance our understanding of possible mechanisms for promoting high-quality professional development.