The study of children’s behavior problems has been hampered by the absence of a classification system, based on empirically identified clinically and theoretically relevant dimensions of children’s behavior, within which research findings could be integrated (Achenbach & Edelbrock, 1978; Thompson, 1986; Thompson, Kronenberger, & Curry, in press). With a satisfactory classification system, questions critical to the development of a behavioral-science knowledge base about children’s behavior problems can be addressed. These critical questions include: What types and frequencies of behavior problems are demonstrated by normal children and by subgroups of children with developmental, medical, or learning problems; how do behavior problems in the various subgroups change over time; what is the association between behavior problems in early childhood and later adjustment; when and with what types of behavior problems is intervention necessary and effective? (Thompson, 1986). Moreover, a satisfactory behavior classification system would enable the study of children’s behavior problems to proceed to theoretically driven research that seeks to evaluate the transaction of biological and psychosocial processes in the etiology, prevention, and remediation of behavior problems (Thompson, 1985a; 1986; Thompson et al., in press).