Guided by the ecological model of civic development, this study examined the extent to which the growth in children's self-control during middle childhood predicted their civic engagement at age 26 directly and indirectly via their prosociality at age 15. We used data from 1,042 children (50% female, 77% White) in the NICHD Study of Early Child Care and Youth Development. Children's self-control at 3rd grade and growth in self-control from 3rd to 6th grade were significantly and positively associated with voting at age 26. In addition to these direct links, children's self-control at 3rd grade and growth in self-control during middle childhood positively predicted children's prosociality at age 15, which, in turn, positively predicted engagement in environmental causes, political or social action groups, and volunteering at age 26. These findings indicate that children's self-control during middle childhood may be an important foundational asset for later prosociality and unique types of civic engagement and may be a key factor for nurturing the development of well-rounded citizens.