Randomisation
A stratified method of randomisation was used with each local authority representing a separate strata. Randomisation was at school level. The intervention was a 2 × 2 factorial design, with schools within each strata randomly assigned to one of four interventions arms, one for each combination of interventions. For every school, a random number between − 1 and 1 was drawn from a uniform distribution. The schools were ordered according to the random number that had been generated for them; then the lowest 25% were assigned to Arm 1, the next 25% Arm 2 and so on. This was done separately for each strata. We did not know at the time of randomisation which schools had email/SMS systems, so we did not include this in the randomisation.Providers knew which school was in each arm, but neither the schools nor the parents who received the interventions knew that they were in a trial.