This quasi-experimental, mixed methods study explored student perceptions of class climate before and after implementation of a two-week social and emotional learning (SEL) intervention in elementary classrooms in Japan. The sample consisted of 131 second and third grade students. A one-time SEL lesson focusing on offering kind words to peers was implemented in three classrooms. This was followed by two weeks of reinforcement, in which students were reinforced each time they offered kind words to a peer. One classroom used a sticker chart as the reinforcement and two classrooms filled up a jar with fuzzy balls. One classroom served as the control. Pre and post surveys were administered to students at the beginning and end of the intervention and teachers completed a survey at the end of the intervention. One-way ANOVA, t-test, and qualitative analyses revealed a significant improvement in class climate, in particular, sense of classroom orderliness, for the classrooms that used fuzzy balls as the reinforcement. Teacher feedback on the implementation of the SEL intervention included both positive and constructive reflections. These results may be considered for the development of SEL curricula to enhance its utility and effectiveness for East Asian student populations.