\ud The Development of Aggression from Ages 2 to 9.5 in a High Risk Sample of Males and Females: Similarities and Differences in Patterns, Predictors, and Outcomes \ud

Abstract\ud Sex differences in base rates of aggression are well-established, with males showing higher levels from preschool-age through adulthood. Research investigating the etiology of these sex differences in base rates of aggression has the potential to inform basic science and prevention. A growing body of work has produced relatively consistent results showing that boys possess a greater number of child-level risk factors for aggression beginning in early childhood; however, findings are less consistent with respect to whether associations between risk and aggression are stronger in boys than in girls. The current study aimed to advance our understanding of associations between early childhood risk and the development of aggressive behavior, as well as the middle childhood consequences of early-starting aggression, in a sample of 731 boys and girls recruited at age 2 for being at high risk of developing conduct problems. Children were followed longitudinally to age 10.5 utilizing multiple data collection techniques including parent and teacher reports, home observation, and structured assessments of child behavior and parent-child interaction. The findings showed that a small proportion of both sexes exhibited high and persistent trajectories of aggression from early to middle childhood and that boys (13.3%) were more likely to exhibit this pattern than girls (6.9%). Toddler-age child-level risk factors for aggression (e.g., low inhibitory control, language delays) were more prevalent in boys than in girls, but no sex differences were observed with respect to base rates of contextual risk factors (e.g., parent depression, parent-child coercion). Associations between toddler-age risk and trajectories of high persistent aggression were not stronger in boys than in girls. A pattern of high persistent aggressive behavior was associated with a broad array of impairments during middle childhood for both sexes, including externalizing and internalizing problems, as well as difficulties in social domains. \u