Ethics clearance was obtained from the Royal Children’s Hospital, University of Melbourne, Department of Education and Training (for public schools) and the Catholic Education Office. Active parental consent was obtained prior to participation, and the consent of parents was reaffirmed in 2006 (using passive consent). Data collection involved a two-stage sampling strategy. In the first stage, within each state and grade level, public and private schools were randomly selected using a probability proportionate to grade-level size sampling procedure [32]. A target classroom within each school was randomly selected in the second stage. Further details about recruitment and participation rates are described in McMorris et al. [27].
