Teacher report of adolescent externalizing behavior and the subscales of rule breaking/delinquency and aggression at ages 15–17 years were assessed using t-scores from the Teacher Report Form (TRF) developed by Achenbach (1991). Teacher report was selected because it reflects behavior in the environment where peer interactions often take place and it is not confounded with the environmental measure (involvement with delinquent peers) reported by the subject. Moreover, the TRF has been demonstrated to be the best predictor of referral for mental health services compared to mother-, father-, or self-reports (Stanger and Lewis 1993). The test–retest reliability of the TRF for problem scores was found to be high (0.92) over a mean interval of 15 days. Stability was good over a 2- or 4-month period. Interrater agreement was similar for teachers seeing pupils under different conditions (r = 0.54 for problem scores).
