Research Findings: This meta-analysis examined 29 (quasi-)experimental studies that involved low-income children ages 3 to 5 who might be subject to risks of academic failure and other negative outcomes. Compared to the controls, children who learned with social-emotional learning (SEL) curricula demonstrated significantly improved social-emotional competence, with an effect size or standardized mean difference of 0.241 (95% confidence interval [0.194, 0.287]). However, the use of other curricula that lacked an intensive focus on SEL yielded nonsignificant effects on the social-emotional competence of low-income children. Type of curriculum, fidelity of curriculum implementation, and duration of intervention were found to moderate the educational effects. Practice or Policy: The findings of this meta-analysis contribute to the growing body of empirical evidence on the positive effects of early SEL curricula and explain how curricula can produce social-emotional benefits for low-income children in their early years.