Developmental trajectories of peer-nominated aggression, risk factors at baseline, and outcomes were studied. Peer nominations of aggression were obtained annually from grades 1 to 3. Three developmental trajectories were identified: an early-onset/increasers trajectory with high levels of peer-nominated aggression at elementary school entry and increasing levels throughout follow-up; a moderate-persistent trajectory of aggression in which children were characterized by moderate levels of physical aggression at baseline; and a third trajectory with stable low levels of aggression. Children following the early-onset/increasers trajectory showed physical forms of aggression at baseline. Male gender and comorbid attention deficit/hyperactivity problems, oppositional defiant problems and poor prosocial behavior plus negative life events predicted which children would follow the earlyonset/increasers trajectory of aggression. The outcomes associated with the early-onset/increaser children suggest high risk for chronically high levels of aggressive behavior.
KEY WORDS: developmental trajectories; conduct problems; peer nominations of aggression; risk factors.Childhood aggressive behavior is a strong predictor of serious negative health and psychosocial outcomes. These outcomes include depression, conduct disorder, antisocial behavior, substance abuse, peer rejection, poor school performance, school dropout, and poor job performance (Caspi, Moffitt, Newman, & Silva, 1998; DeaterDeckard, 2001;Loeber, Green, Keenan, & Lahey, 1995;Moffitt, Caspi, Dickson, Silva, & Stanton, 1996;Moffitt, Caspi, Harrington, & Milne, 2002;Nagin & Tremblay, 1999). Despite the high stability of aggressive behavior from childhood into adolescence and young adulthood, many aggressive children will not persist in this behavior. Tremblay et al. (1999) reported for instance that 80% of all 17-month-old toddlers showed physically aggressive behavior, whereas in a cross-national study on the development of aggressive behavior, 4-11% of all children were found to follow a chronic physically aggres-