The authors note that research on the influence of peers in the emergence and reinforcement of aggression has been weak. They advise that greater attention to the role of the peer group is important for understanding the nature of risk and protective factors for various types of aggression. The research to date shows that physical aggression is typical in the preschool years. It declines in subsequent years as verbal and social forms of aggression emerge and become stable with age; however, developmental trajectories within this broad pattern differ for boys and girls. Physical aggression is more prevalent in boys than in girls beginning in the elementary- school years and persisting throughout adolescence. Some research shows that boys are also more likely to use verbal aggression than girls; whereas, girls are more likely than boys to use social aggression (tactics of social exclusion and isolation against their targets of aggression). Within these broad age-related and gender-related patterns for various types of aggression, however, are the influences of individual characteristics, both biological and psychological; social influences (behaviors and attitudes of parents and peers); and broader societal and media influences. 106 references