Background:
In Danish vocational schools the prevalence of daily smoking is particularly high (nearly 40%). Schools are increasingly implementing school tobacco policies (STP). However, studies on the effects of STP are inconclusive, and not all elements of STP may be equally effective. Our objectives were to describe STP characteristics and practices, and examining the associations between STP and students' smoking behaviour.

Methods:
This study used data from Danish National Youth Study 2014. Participants were 5,013 vocational school students (median age=19.1; 76% male) at 40 campuses. Implementation of STP was measured by principal questionnaires and field observations. Multinomial logistic regression models assessed whether STP characteristics and practices were associated with students' daily and occasional smoking compared to non-current smoking. Negative binominal regression models assessed cigarettes per day among daily smokers.

Results:
All schools had an official tobacco policy. Fourteen (35%) campuses had complete smoking ban. The majority (87%) had implemented sanctions for breaking smoking rules; however, student smoking was observed on 78% of campuses. Students attending schools with sanctions were less likely to smoke daily (odds ratio=0.82, 95% confidence interval: 0.70, 0.97) and fewer cigarettes were reported among daily smokers (14.9 versus 16.0, p< .05). Occasional smoking was lower (odds ratio=0.72, 95% confidence interval: 0.55, 0.92) for students attending schools with comprehensive focus on tobacco restriction and prevention programmes compared to those without comprehensive STP. Conversely, occasional smoking was 1.3 times (95% confidence interval: 1.1, 1.6) higher for students attending schools with visible student smoking. These associations were not found for daily smoking. There were no significant findings for sale of cigarettes on campus.

Conclusions:
Dimensions of STP were related to smoking behaviour in different ways. These findings support the need for additional research focusing on how elements and practice of STP impact on various stages of smoking progression among young people.