A majority of research investigating aggression and its development in children relies on rating scales such as the Child Behavior Checklist (CBCL). These scales typically are developed using a conventional factor analytic approach for the selection and retention of scale items, but may contain insufficient items to assess the unidimensionality and developmental trajectory of youths’ aggressive behavior. Rasch analysis was employed to determine the extent to which CBCL Aggressive and Delinquent clinical syndrome scale items reflect the unidimensionality and expected developmental trajectory of aggressive behavior based on parent endorsements of 455, 6 to 16 year old boys referred to community mental health centers. The two scales showed considerable promise as a unidimensional aggression scale and mimic the expected developmental pattern of aggressive behavior in extant literature. Future development of an aggressive CBCL dimensional subscale, however, must eliminate redundant and non-contributing items, and include severe aggressive behavior items exhibited by persistently aggressive youths.