This study examined emotional reactivity to rejection and executive function (EF) skills as potential mediators of the social behavior problems of inattentive and hyperactive kindergarteners. Participants included 171 children, including 107 with clinical levels of ADHD symptoms, 23 with sub-clinical levels of ADHD symptoms, and 41 typically developing children (63 percent male; 73 percent Caucasian, 11 percent African-American, 4 percent Latino/Hispanic, 1 percent Asian, and 11 percent multiracial; Mage= 5.2 years). Inattention (but not hyperactivity) was uniquely associated with poor EF, social withdrawal, and aggression. In structural equation models, EF skills mediated the associations between inattention and both aggression and social withdrawal. Hyperactivity (but not inattention) was uniquely associated with rejection reactivity and each contributed uniquely to aggression. Findings suggest that difficulties with emotion regulation may warrant more attention in early interventions planned for children with high levels of ADHD symptoms.