In a previous study, reactive criminal thinking or cognitive impulsivity mediated the relationship between parental knowledge and delinquency. This study sought to determine whether cognitive impulsivity also mediated the relationship between parental knowledge and childhood aggression. A path analysis was performed on a sample of 438 early adolescent boys (n = 206) and girls (n = 232) from the Illinois Study of Bullying and Sexual Violence using three waves of non-overlapping data. As predicted, cognitive impulsivity mediated the relationship between parental knowledge and childhood aggression, but cognitive insensitivity did not. The results of this study provide ongoing support for the general conceptual argument that childhood aggression parallels delinquency in certain respects and that parental knowledge deters both future delinquency and childhood aggression by reducing the cognitive impulsivity that is central to the behavioral patterns of delinquency and childhood aggression.