Children and adolescents between 6 and 15 years of age were asked to report on typical same-sex peers' aggressive responses to a hostile act that had occurred in dyads and groups that were either compatible or incompatible. Results demonstrated that females were expected to display the highest levels of aggression in compatible one-on-one relationships as opposed to in compatible group relationships or in incompatible relationships. Males did not differ across the type of relationship in the level of aggression that they were expected to display. The connection between investment in a relationship and aggression is considered.