2.4. Procedure
2.4.1. Data generation
Ethical approval for the study was given via the University of Manchester Ethics Committee and informed consent for participation was obtained from parents and teachers at the outset of the study. At Time 1 (T1) the WOST was completed for each child by a key teacher (i.e. someone who knew the student well). This survey was repeated 18 months later at Time 2 (T2). During the interim period all additional explanatory variables at school and individual level were collected.