RESUMO
Background: Low academic achievement has been associated with smoking but factors behind this association are poorly known. Such factors could include schoolwork disengagement and schoolwork difficulties. To assess the extent to which they contribute to the explanation of how health inequalities emerge, we study in a longitudinal design whether these have an independent effect on smoking or whether their effect is mediated through academic achievement. Methods: Longitudinal data were collected in the Helsinki metropolitan area, Finland in 2011 and 2014. Participants were seventh-graders (12 - 13 years, N=9497). In the follow-up, 6534 students reported their smoking status in the ninth grade (15 - 16 years). Smoking, schoolwork behavioural engagement, i.e. participation in academic activities, and disengagement, schoolwork difficulties and cognitive competence were self-reported by adolescents. Academic achievement was obtained from the Finnish national application register on upper secondary education. A mediation analysis was executed with bootstrapped confidence intervals. Results: Higher schoolwork behavioural engagement and cognitive competence in the seventh grade predicted that adolescents were more likely not to smoke in the ninth grade (all P<0.001) while higher schoolwork disengagement and schoolwork difficulties predicted adolescents' smoking (all P<0.001). The effects were mediated through academic achievement. Conclusions: Students' behavioural disengagement with schoolwork and schoolwork difficulties are risks for smoking initiation. Their effect is mediated through poor school achievement. As smoking often continues in adulthood and poor school performance typically leads to lower education, schoolwork disengagement and difficulties in adolescence constitute potential pathways to inequalities in health.