The relationships between sport involvement variables (participation and interest) and facets of children's morality (reasoning maturity and aggression tendencies) were investigated for 106 girls and boys in grades 4 through 7. Children responded to a sport involvement questionnaire, participated in a moral interview, and completed two self-report instruments designed to assess aggression tendencies in sport-specific and daily life contexts. Analyses revealed that boys' participation and interest in high contact sports and girls' participation in medium contact sports (the highest level of contact sport experience they reported) were positively correlated with less mature moral reasoning and greater tendencies to aggress. Regression analyses demonstrated that sport interest predicted reasoning maturity and aggression tendencies better than sport participation. Results and implications are discussed from a structural developmental perspective.