This is a community essay to assess the effectiveness of a multi-level (individual, family, and school) school-based intervention to prevent the exposure to secondhand smoke (SHS) in a population of 1,734 schoolchildren (12-14 years old) in Terrassa (Catalonia, Spain). Schools were assigned to the intervention or the controlgroup at random. The investigators assessed SHS exposure in different settings (at school, at home, on transportation and leisure time) and tobacco consumption by means of a questionnaire before and one year after the intervention. Based on a previously evaluated intervention to prevent smoking initiation (PASE/ESFA program) the investigators designed a new intervention (the RESPIR•NET Program) including two new activities to prevent passive smoking to be applied at three levels: in the classroom (pupils), at the school (pupils, teachers, and parents), and in the family (pupils and parents).