This study examined the association between school bonds and the onset of substance use among adolescents in South Korea. Based on Hirschi’s social control theory, this study tested the roles of teacher attachment, educational aspiration, extracurricular activities, and rule internalization—four elements of social bonds within the school setting—in delayed initiation of alcohol drinking and cigarette smoking. Discrete-time logistic regression was used to analyze five waves of the Korea Youth Panel Survey (N = 3449 at baseline), a nationally representative sample of Korean youth. Stronger teacher attachment, higher educational aspiration, and higher rule internalization were correlated with delayed onset of alcohol drinking and cigarette smoking. On the other hand, participation in school extracurricular activities was positively associated with the onset of alcohol drinking, but not statistically significantly linked with the onset of cigarette smoking. These findings suggest that early prevention strategies for youth substance use should specifically target school-related factors that represent social bonds developed among youth.