Table 6 Data collection barriers

Some schools allowed pupils to take follow-up questionnaires home, rather than complete during class time, and this strategy was associated with lower response rates

Further encourage schools to ensure follow-up questionnaires are completed during school time, e.g. registration

There was strong feedback from schools to avoid any data collection in the summer term so that clashes with examinations could be avoided

The timelines for each school were bespoke depending on their enrolment date and when the pupils were randomised. The timelines for each school, however, took into account the necessity to avoid times that were considered high stakes by the schools while still fitting in with the timelines required for the trial

Difficulties organising mutually agreeable dates for baseline dental assessments between the schools and LRTs

LRTs to try to complete a timeline of planned trial activities with the school, including planned dates for baseline data collection, at trial entry

Impact of a spell of severe weather conditions, e.g. resulting in school closures

No solution possible

Dental assessments require space and privacy and therefore the need for a room to be available in school for the duration of data collection which was not timetabled for other use

This was achieved by careful discussions with senior management teams — experience from pilot trial informed how we approached schools and what we asked for in main trial