Measures
HOLIDAY
Baseline data were collected at the semester start after the summer holiday (August). Here, students completed a digital questionnaire during school hours about smoking, attitudes towards smoking, sociodemographic questions as well as other health and well-being related questions. At the same time, teachers and principals answered a baseline data questionnaire about smoking at their schools, rules, etc. A longitudinal follow-up assessment was performed approximately five months after baseline among students (December), and prior to this follow-up assessment, school principals and teachers in intervention classes answered a questionnaire about the implementation of the intervention (November).All question framings and definitions of variables used in this study are in detail described in Additional file 1.