The effect of classroom aggression-related peer group norms on students' short-term trajectories of aggression.

Using a four-wave/seven-month longitudinal design with a sample of 1595 preadolescents (53% boys, 47% girls, M  = 10.2 years) from 63 fourth-, fifth- and sixth- grade classrooms in nine mixed-sex schools in Bogotá, Colombia, we examined whether growth trajectories of measures of overt and relational aggression varied as a function of classroom norms for aggression. Multilevel growth mixture modeling revealed (a) distinct trajectories of overt and relational aggression for boys and girls and (b) that norm salience (i.e., the process by which a group norm is made salient via the punishments or reinforcements to the behavior within the group) was a better predictor of associations with trajectories of overt and relational aggression than were perceived injunctive norms (i.e., the perceived standards of what is approved or disapproved in a social context). In classrooms where popular or accepted children were perceived by their peers as aggressive, more boys followed an increasing trajectory of overt and relational aggression than a low-stable trajectory, and more girls followed a high-stable trajectory of relational aggression than a low-stable trajectory. These findings are discussed in terms of the practical implications for the design of educational interventions aimed at preventing aggression in classroom settings.