"Second Step" is a universal social-emotional learning program designed to decrease antisocial behaviors, increase prosocial behaviors, and increase knowledge about content curriculum. Given the international focus of using Second Step to improve social-emotional skills, it is especially important to provide an updated synthesis on the effect of the intervention. A single-program meta-analysis was completed in order to determine effects of participating in Second Step and to explore moderators of program effectiveness on prosocial and antisocial behavior outcomes as well as knowledge of emotions. Five moderators were explored, including (a) program saturation, (b) dependent variable source, (c) grade range, (d) metro area, and (e) geographical location. A combined total of 18,847 participants were included in the analysis of 27 studies. Results of the current study indicate that "Second Step's" impact on students' knowledge and attitudes of violence and violence prevention is much stronger than on increasing prosocial behavior or reducing antisocial behavior.