The word “character” has generally lost its currency in the literature on personality and social psychology over the last 20 years. And yet the assumption that sport builds character is still held, at least privately, by a great many people. This investigation was an attempt to reconsider the “character” construct, to isolate its social elements, and to establish its susceptibility in childhood to the influence of organized sport experience. Using prosocial behavior as one manifestation of evolved social character, the influence or organized sport was assessed in a field experiment with children from two elementary schools. Although the general assumption that “sport builds character” was not strongly supported or refuted in this investigation, some evidence, at least with males, showed that prosocial behavior may be inhibited by sport experience. Finally, implications were drawn for facilitating prosocial behavior in children's sports.