As was expected, boys for whom onset was early (their first registered offense before the age of 13) manifested educational difficulties and externalizing problems in early school grades (at the ages of 10 and 13) to a greater extent than other boys, and they also exhibited such problems at the age of 15. Educational and externalizing problems were most manifest at the age of 15 among the group of boys with middle adolescent onset of official delinquency. Boys with early and middle adolescent onset had school and conduct disturbances in common at the age of 15, had frequent peer contacts in both early and late grades, and perceived their peers as endorsing norm-breaking. In comparison with boys who were not registered by the police for some offense up to the age of 16, they had lower IQs, lower socioeconomic status, and a higher frequency of dropping out of school. Boys with early adolescent onset of offending had poor relations throughout school. Boys with middle adolescent onset of offending displayed less evidence of poor peer relations in early grades, and they had many close friends, friends at school, and same-age friends at the age of 15. Boys with middle adolescent onset of offending were characterized by a history of not living together with their natural parents. The authors discuss study results against a background of distinctions between unsocialized, aggressive, and socialized delinquency and previous research on peer status at school. Footnote, tables, figures, references