The purpose of the present study was to examine the impact of sex, verbal reasoning, and normative beliefs on direct and indirect forms of aggression. Three scales from the Peer Estimated Conflict Behavior Questionnaire, Verbal Reasoning tests, and an extended version of Normative Beliefs About Aggression Scale were administered to 663 Estonian students (289 boys and 374 girls; 150 fifth, 264 seventh, and 249 ninth graders; ages 11-16). Self- and same-sex peer ratings were used to assess the frequency of aggression. Associations between study variables were examined using structural equation modeling. Results showed that boys had higher levels of physical and verbal aggression in all the grades and higher levels of indirect aggression in Grade 7. Verbal reasoning predicted negatively all the forms of aggression, except for indirect aggression in Grade 7. Normative beliefs had a positive effect on all three forms of aggression in Grade 7 and Grade 9.