Poor inhibitory control and bold approach have been found to predict the development of externalizing behavior problems in young children. Less research has examined how positive affect may influence the development of externalizing behavior in the context of low inhibitory control and high approach. We used a multi-method approach to examine how observed toddler inhibitory control, bold approach, and positive affect predicted externalizing outcomes (observed, adult-, and self-reported) in additive and interactive ways at the beginning of kindergarten. Children who were 24-month-olds (N = 110) participated in a laboratory visit and 84 were followed up in kindergarten for externalizing behaviors. Overall, children who were low in inhibitory control, high in bold approach, and low in positive affect at 24 months of age were at greater risk for externalizing behaviors during kindergarten.