Although police and court records rarely reflect the prevalence of conduct problems and delinquency in elementary schoolchildren, a review of parent-, teacher-, and self-reports for prehigh school fighting, theft, truancy, vandalism, marijuana use, and delinquency indicate that a small but significant proportion of young boys and girls engage in such behaviors and these behaviors may presage the onset of delinquent careers. In addition, early onset of such behaviors is salient in predicting adult offending and chronic offending. Policy implications of these prevalence and correlative data are discussed with reference to criminal responsibility, juvenile justice response, and intervention. Substantial tabular data summarize existing research into the prevalence and correlates of serious conduct problems in this age group. 5 tables, 3 footnotes, and 52 references. (Author abstract modified)