- Existing theory and empirical data suggest that clinically meaningful distinctions may be made among aggressive youth during middle childhood based on their self-systems (i.e., their perceptions of their own competencies and of the extent to which they believe they are supported, valued, or esteemed by others). Most aggressive children appear to have self-systems that are more polarized and rigid (i.e., either globally positive or globally negative) when compared to nonaggressive children. Further, those who overestimate their level of competence and the actual quality of their (usually impaired) relationships with significant others appear to be at greater risk for increased behavior problems than those aggressive children who more accurately perceive their competence deficits and relationship difficulties. Tentative hypotheses are offered regarding developmental changes in the relationship between the self-system and aggression as these children mature into adolescence and adulthood. Implications for classification, assessment, and treatment matching are discussed.