This study explored students' prosocial efficacy and reading outcomes in a culturally relevant summer reading program for underrepresented students. From a positive developmental approach, the reading program focuses on topics rooted in multicultural education, with books organized according to themes such as making a difference for oneself, one's family, the community, the country, and the world. In the mixed-method study, we analyzed the results of students' surveys and reading tests (n = 87) and interviews with two teachers and a program coordinator. Students' initial prosocial efficacy was positively related to reading test scores at the end of the intervention; the positive linking between the two variables was more remarkable in the younger children group and with female students. The supplementary findings from the interview analysis of adult participants (teachers and staff) indicate that underrepresented students from culturally relevant education are more likely to experience a higher sense of belonging and show greater reading engagement related to various social issues. This study's findings provide valuable insights into what strategies of the SEL approach should be considered to support the social-emotional and academic growth of underrepresented students in future education.