Absolute prevalence of tobacco smoking has fallen in recent decades but inequalities by socioeconomic position (SEP) persist. Adolescence is a critical period for smoking initiation and habits formed during this period likely continue into adulthood. Explanations for inequalities in adolescent smoking have tended to focus on individualistic theories based on differentials in knowledge and psychology. These have been criticised for their blindness to processes of social stratification and social context that influence smoking behaviours. Based on previous social theories, we put forward, and test empirically, two potential structural explanations for inequalities in smoking, using nationally representative longitudinal cohort data on 6039 Irish young people aged 9-18 years. Descriptive analyses confirmed the adverse SEP gradient in smoking prevalence as well as SEP gradients in variables representing individual-level characteristics and structural-level explanations. Despite lower self-esteem being associated with a higher likelihood of smoking, there was no significant indirect pathway between SEP and smoking via self-esteem. Path analyses found that differentials in exposure to parental smoking and levels of oppositional values mediate the relationship between SEP and smoking. Our results favour structural and group-based explanations for inequalities, that is, the 'smoking exposure' and 'social resistance' models, over explanations based on individual psychology.