This study extends the opportunity theory of victimization to consider the social capital of adolescents at school. We argue that social capital might act as a protective factor potentially encompassing both the concepts of guardianship and target attractiveness. Drawing on a sample of 5395 adolescents interviewed in the context of the 2007 National Crime Victimization Survey (school crime supplement), we develop school-specific measures of social capital and opportunity indicators in predicting violent and theft victimization on school grounds. The results show that opportunity indicators are strong predictors of both violent and theft victimization and that social capital is especially important as a protective factor from violent victimization. More specifically, the results indicate that students who developed trust relationships with adults at school benefit from these relationships by avoiding violent encounters with potential offenders. Implications for opportunity theories of victimization are discussed.