A stable aspect of adolescent property offending has been coincidence of the peak age of such offences with the last year of compulsory schooling. This fact is taken as the focus of three epidemiological analyses. These were: 1. A survey of child welfare records of adolescent property offences for Hamilton, N.Z., in 1971. 2. The collection of teacher ratings of behaviour for a delinquent sample and a random sample, in the classroom situation. 3. Investigation of an unexpected finding, the disappearance of the peak age in Scotland in 1961. Study 1. confirmed earlier work suggesting that the property offences of the younger adolescent are more likely to be first offences and of a casual, low expertise nature. It added to such findings the fact that this is not so much an age effect as a difference between those attending school and those who have left school. Study 2. replicated the well established finding of close association between difficult behaviour at school and delinquent acts. It added to such studies the fact that while property offending increases rapidly in early adolescence, difficult behaviour remains fairly stable. Study 3. provided an unusual example of variation in delinquency rates, and showed that children born immediately after World War 2 in Scotland were significantly less delinquent than expectation. The results of these studies are extensively discussed in relation to a general concept of primary deviance, the interaction between socialisation and situational or life style variables, and the nature of socialisation processes.