A selectionist theory states that violence by males toward male peers originally served specific functions and violence to female peers served others. Differences in self-reported victimization and perpetration in studies of 1.452 high school students were hypothesized. In Study 1, male-to-male aggression was reported to be more prevalent than male-to-female aggression. For male-to-male aggression, perpetrator reports agreed with or exceeded victim reports, and victims were more often strangers than close friends, In contrast, for male-to-female aggression, there were consistently fewer reports from perpetrators than from victims, and victims were less often strangers than girlfriends. Study 2 obtained similar findings for reported frequency, number of victims and perpetrators, and sexual aggression. Study 3 showed that girls' aggression contrasted with that by boys with respect to intra- versus intersex aggression and perpetrator victim agreement.