Demographics
Parental education and children’s sex, age, and migration background were assessed at baseline by a parental (or legal guardians) questionnaire. This questionnaire was provided in seven different languages and was handed out by the teachers to all participating children. Children were asked to give the questionnaire to their parents and to return the completed questionnaire at school and to give it back to their teacher. The research team collected all completed questionnaires at schools. If information on education was available from both parents/legal guardians, parental education was classified into low, medium, and high according to Lampert et al. [