It has been proposed that aggressive behavior may result from unrealistically positive self-evaluations that are disputed by others (Baumeister, Smart, & Boden, 1996). The present three studies tested this proposition concurrently and longitudinally for the domain of self-perceived social competence (SPSC) in 3–6th grade children on two continents. Each study tested whether aggressive behavior is related to general overestimation of SPSC compared to competence as perceived by peers, or to disputed overestimation, that is, overestimation disputed through rejection by peers. Specificity of relations with reactively or proactively aggressive behavior patterns was assessed and the predictive value of overestimation to the development of these types of aggressive behavior was investigated. Concurrently, disputed overestimation explained more variance in aggressive behavior than general overestimation, and was uniquely related to proactive aggression. Longitudinally, disputed overestimation also uniquely predicted changes in proactive, not reactive aggression.