Two main research questions were posed: (1) did schools vary in offending rates among pupils, and (2) what factors caused and predicted offending by pupils in the school context? Main findings indicated that offending among students in schools was generally restricted to less serious crimes, with the most common crimes being assault, theft, and vandalism. Males were more likely to be involved in criminal activities in schools than were females and those who were frequent offenders also tended to be versatile in their offending habits. The findings also indicated that students who offended in school were also more likely to be victimized in school. Wide variations in students’ prevalence and frequency of offending rates between schools were observed, indicating that the school a student attended might significantly impact his or her chances of exposure to crime, either as an offender or as a victim. Other findings revealed that: (1) students’ residential neighborhood was weakly associated with offending in schools; (2) students’ family social position was weakly associated with their offending behavior in schools; (3) students’ view of school context was significantly related to offending in schools; (4) students’ social situations and dispositions were strong predictors of their risk of offending in schools; and (5) students with individual risk-protective characteristics were more likely to report offending in schools that displayed many contextual risk factors. The Cardiff School Study was a cross-sectional, self-report study of 3,103 Year 10 students (aged 14 to 15 years) who were enrolled in the 20 state comprehensive schools in Cardiff. The self-administered questionnaire asked about offending and victimization in school, as well as about risk and protective factors. Future research should employ longitudinal research methods to further investigate student offending patterns as well as the reasons students offend in schools. Figures, tables, references, index