The replication data came from the Denver Youth Survey and the Rochester, N.Y., Youth Development Study. Restrictions on data availability meant that the research could assess only physical fighting and violence in the Overt Pathway and property damage, moderately serious delinquency, and serious delinquency in the Covert Pathway. Results revealed the expected pattern at each site; the less serious forms of problem behavior and delinquency occurred first, and the more serious forms of the behavior occurred later. The best fit for the Covert Pathway was before age 15; the Overt Pathway had a better fit than the Covert Pathway across the three sites. The sites differed in the percentage of boys in the overt and covert pathways. However, the percentage who persisted in the joint overt and covert pathway ranged from 21 percent to 35 percent. Overall, findings reveal that males who report the onset of delinquent behavior prior to age 11 are more likely to offend and to be more frequent, persistent, serious, and wide-ranging offenders than those who start after age 11. Findings indicated that preventing the acceleration of juvenile delinquency and other co-occurring problems in very young children is clearly an important policy and program priority. Figures, tables, and 20 references