This study examined whether peer norms for aggression within the classroom impact friendship selection, maintenance, and socialization processes related to aggression across the 1st year of secondary school (N = 1,134 students from 51 classes, Mage = 12.66). As hypothesized, longitudinal social network analyses indicated that friendship selection and influence processes related to aggression depended on the popularity norm within the classroom (i.e., the class‐level association between popularity and aggression) rather than the descriptive norm (aggregated average of aggressive behavior). Hence, only in classes where the valence of aggression is high (because it is positively associated with popularity), adolescents tend to select their friends based on similarity in aggression and adopt the aggressive behavior of their friends.