Background: More research is needed to improve measurement selection and to better understand informant differences in reports of reactive and proactive aggression. Objective: Toward this goal, the current study evaluated the psychometrics (i.e., reliability, factor structure, and validity) and correlates of two measures of reactive and proactive aggression (i.e., Dodge & Coie, in J Pers Soc Psychol 53:1146, 1987; Raine et al. in Aggress Behav 32:15-171, 2006) across three informants (i.e., parent, teacher, and youth). Method: Parent, teacher and youth reports of measures were collected in a community recruited sample of 9-12 year-old youth (M = 10.44; 56% male). Results: Both measures demonstrated adequate to good internal consistency by parent- and teacher-report, and borderline to adequate internal consistency by youth-report. Additionally, aggression subscales were correlated within and across measures and informants, and an appropriate 2-factor structure was identified for both measures across informants. Consistent with prior research, reactive aggression was more robustly associated with depression symptoms and effortful control than proactive aggression across measures, but there were some links with proactive aggression. Conclusions: Overall findings suggest that both measures are psychometrically appropriate to use with parents, teachers, and youth. However, there were distinctions between the two measures, and relying solely on youth reports in this age group is not recommended. Further, there are unique associations evident with various informants, supporting the need for multiple informants when assessing functions of aggression in youth.