Drawing upon ideas stemming from social disorganisation theory, this study explores how structural and social aspects of the school context affect youth substance-use behaviours in terms of smoking, alcohol and/or drug use. A key focus is to investigate the joint effect of school collective efficacy and schools' substance-use norms on students' substance use. Analyses are based on combined information from two independent data collections conducted in 2014 among ninth grade students (n = 5122) and teachers (n = 1105) in 81 senior-level schools in Stockholm. Results from multilevel analyses confirm previous research by suggesting that the proneness to engage in substance use varies depending on the socioeconomic profile of the school. Youth in socioeconomically advantaged schools were more prone to engage in substance use than youth in disadvantaged school settings. Furthermore, collective incentives for exerting social control against substance use seem to be weaker in schools where conventional values towards substance use (anti-substance-use norms) are suppressed.