Whereas previous research suggests that adolescents’ aggressive behavior in itself does not highlight ethnic boundaries, it remains unclear whether classmates’ responses to same- and cross-ethnic aggression strengthen ethnic boundaries. This study examined how adolescents’ aggression toward same- and cross-ethnic peers relates to the positive (friendship) and negative (rejection) relationship nominations they receive from same- and cross-ethnic classmates. Cross-sectional peer nomination data on 917 Dutch and 125 Turkish adolescents in 56 secondary schools were analyzed (mean age = 14.9 year; 51.4% boys). Adolescents received more friendship nominations from same-ethnic than from cross-ethnic classmates, but were not more rejected by cross-ethnic than same-ethnic classmates. Multilevel Poisson and negative binomial regression models showed that, irrespective of aggressor’s ethnic background, adolescents’ aggressive behavior was related to rejection by classmates from the ethnic group that was the target of aggression and to being befriended by classmates from the ethnic group that was not the target of aggression. Specifically, both Dutch and Turkish adolescents who were aggressive toward Dutch peers were rejected by Dutch classmates and befriended by Turkish classmates and vice versa. These findings suggest that classmates’ positive and negative responses to adolescents are related to adolescents’ aggressive behavior based on the ethnic background of the victim, not on the ethnic background of the aggressor. This suggests that integration between ethnic groups in schools relates to aggression in general, not only cross-ethnic aggression.