Traumatic stress exposure has been identified as a robust risk factor for atypical cognitive development in childhood. While most research focuses on neurological mechanisms underpinning these relationships, peer influences may also provide a social mechanism. The present study examined deviant peer association as a mediator in this regard within the context of the dual systems model in childhood and adolescence. The Adolescent Brain Cognitive Development data were analyzed. Structural equation modeling was used to analyze direct and indirect effects of interest. Findings indicated that traumatic stress exposure predicted diminished impulse control, but did not predict sensation-seeking. Deviant peer association significantly mediated the relationship between traumatic stress exposure and impulse control, accounting for about 25% of this relationship. Implications are discussed.