Initiation in offending was most marked for the youngest sample, escalation in the seriousness of offending was prominent for the middle and oldest samples, while de-escalation was most prevalent in the oldest sample. The strength of association between the initial and later seriousness of offending appeared to increase with age. We classified offenders according to their pattern of seriousness of offending over time (called a dynamic classification of offenders). Many variables correlated with this measure, showing a covariation with both increases and decreases in the seriousness of offending over time. We noted major shifts in the correlates of offense seriousness between the three age samples-physical aggression and social withdrawal decreasing in strength, while school problem behaviors, peer deviance, and boys' positive attitude to deviancy increased in magnitude. Several factors were associated with the early initiation of offending (before age twelve), including social withdrawal and depression, positive attitude to problem behavior, association with deviant peers, and family problems. In contrast, the later onset of offending (between ages thirteen and fourteen), among other factors, was associated with low school motivation. Correlates of escalation were found for the two older samples but not for the youngest sample and were particularly prominent in the area of school functioning, disruptive behaviors, positive attitude to deviant behavior, and some aspects of family functioning. Several variables were associated with desistance in offending, including low social withdrawal, low disruptive behavior, and positive motivational and attitudinal factors. The correlates of initiation were distinct from the processes explaining escalation, but were similar to the correlates of desistance. Finally, the paper discusses the relevance of the findings for preventive interventions. 8 figures, 2 tables, and 54 footnotes (Publisher abstract)