Written instructions are provided to the teacher, and
questionnaires are returned in closed envelopes to
ensure anonymity with regard to other students and
teachers. Given the non-invasive nature of the study,
passive informed consent is obtained from parents every
year. More specifically, parents receive a letter with information
about the planned questionnaire study on ‘Internet
use and well-being’. If parents do not agree with
their child’s participation they can inform the school
coordinator and/or the researchers, in which case the
child is excluded from participation. Children can refuse
participation either by informing their parents or their
teachers. Refusal by either parents or children rarely
occurred.