The study examined the effect of National Board Certified Teachers (NBCTs) on social-emotional competencies of fifth and sixth graders in the 2018-19 academic year in Spokane, Washington. The study used archival data and quasi-experimental design with matching to compare social-emotional competencies of students taught by NBCTs and students taught by non-NBCTs. The study examined 10 social-emotional competencies. The results suggest that NBCTs are significantly more effective than non-NBCTs at facilitating students' self-efficacy approximately 2 months after the start of the school year (effect size = 0.21). Results for self-management are in the same direction (effect size = 0.10), however not statistically significant. Findings for the remaining eight social-emotional competencies are not statistically significant, and the effect sizes are small. The results also suggest that NBCTs are effective at developing social-emotional competencies for students who are native English speakers for two social-emotional measures: self-efficacy (effect size = 0.23) and social awareness (effect size = 0.16). The study is the first attempt to rigorously examine the effect of NBCTs on students' social-emotional competencies. Although the evidence is encouraging, additional rigorous research is needed to make confident conclusions, particularly for students who are English language learners and from different racial/ethnic subgroups because of the small number of these students in the current study. [This study was funded by the Supporting Effective Educator Development Grant.]