The current study investigated the patterns of aggressive behavior displayed in a sample of 282 students in the 4th through 7th grades (M age = 11.28; SD = 1.82). Using cluster analyses, two distinct patterns of physical aggression emerged for both boys and girls with one aggressive cluster showing mild levels of reactive aggression and one group showing high levels of both reactive and proactive aggression. Both aggressive clusters showed problems with anger dysregulation, impulsivity, thrill and adventure seeking, positive outcome expectancies for aggression, and higher rates of bullying. However, the combined cluster was most severe on all of these variables and only the combined aggressive group differed from non-aggressive students on their level of callous-unemotional traits. Similar patterns of findings emerged for relational aggression but only for girls.

The current study investigated bullying behaviors in 284 school children in the fourth through seventh grades at the time of the initial assessment. Peer ratings of bullying behavior were obtained at the end of the spring semester of one school year and at the end of the fall semester of the next school year. Importantly, peer ratings were obtained by assessing not only the level at which participants actually bully other students but also whether participants help bullies to hurt the victim (assister), encourage bullies (reinforce), or help the victim of bullying (defender). Our results did not support the utility of differentiating between bullies, assisters, or reinforcers. Specifically, these bullying roles were highly intercorrelated, both concurrently and across school years, and they showed similar correlations with aggression and several characteristics often associated with aggression (i.e., conduct problems, callous-unemotional traits, and positive expectancies about aggression). In contrast, ratings of defending designated a particularly prosocial group of students. Finally, whereas bullying appeared to be very similar in boys and girls, it was somewhat more stable across school years and was related to lower levels of prosocial behavior in boys, both of which could suggest that bullying may be somewhat more related to social group dynamics in girls.

The current study tested whether callous-unemotional (CU) traits explained unique variance in measures of aggression and bullying, and in measures assessing cognitive and affective correlates to aggression, when controlling for conduct problem severity. In a sample of 284 ethnically diverse students (ages 9 to 14 years), a self-report measure of CU traits did not explain unique variance in self-report measures of reactive aggression but did interact with conduct problems in predicting proactive aggression, with conduct problems being more strongly related to proactive aggression in students high on CU traits. Conduct problems were also more strongly related to peer-reports of bullying in girls high on CU traits. Further, CU traits were negatively related to behaviors that defend victims of bullying, independent of conduct problem severity. Finally, conduct problems were more strongly related to anger dysregulation in students low on CU traits, and conduct problems were more strongly related to positive expectations for aggressive behavior in girls high on CU traits. These findings provide support for the proposal to include CU traits as a specifier for the diagnosis of conduct disorder.