Table 1 Feasibility outcomes and criteria for progressing to cluster randomised controlled trial

Negative impacts of the study procedures

• Monitoring participant reports throughout

• Bespoke acceptability questionnaire (child-, parent-, teacher-report)

• Qualitative interviews/discussion groups (children, parents/carers and school staff)

• Study Steering Committee judgement

GO: Serious negative impacts have not arisen at this stage as a result of participation in the study procedures

GO: Serious negative impacts have not arisen as a result of participation in the study procedures

• Implement indicated changes to study procedures to minimise the risk of any negative impacts

STOP: There are serious concerns about harms of study procedures, confirmed by Study Steering Committee

STOP: There are serious concerns about harms of study procedures, confirmed by Study Steering Committee

Acceptability of all study procedures, including screening, feedback for parents/carers, brief intervention

• Monitoring participant reports throughout

• Bespoke acceptability questionnaire (child-, parent-, teacher-report)

• Qualitative interviews/discussion groups (children, parents/carers and school staff)

• Study Steering Committee judgement

GO: No serious concerns have arisen about the acceptability of the study  procedures

GO: No serious concerns about the acceptability of the study procedures

• Implement indicated changes to study procedures to minimise any concerns and maximise acceptability among children, parents/carers and school staff

STOP: There are serious concerns about the acceptability of study procedures, confirmed by Study Steering Committee

STOP: There are serious concerns about the acceptability of study procedures, confirmed by Study Steering Committee

Recruitment and retention rates

• Number (%) of eligible participants who complete baseline and follow-up assessments

• Number (%) of participants who screen positive (target population) who complete baseline and follow-up assessments

• Number (%) of participants who participate in OSI

GO:

• At least 80% of participants who screen positive (target population) complete the baseline assessment.

• At least 12% of parents of children in study classes^a to date participate in OSI

GO:

• At least 80% of participants who screen positive (target population) complete all assessments.

• At least 12% of parents of children in study classes^a participate in OSI

• Implement indicated changes to study procedures to improve recruitment/retention rates

AMEND:

• ≥ 70% and < 80% of participants who screen positive (target population) complete the baseline assessment.

• ≥ 9% and < 12% of parents of children in study classes^a to date participate in OSI

AMEND:

• ≥ 70% and < 80% of participants who screen positive (target population) complete all assessments.

• ≥ 9% and < 12% of parents of children in study classes^a participate in OSI

STOP:

• < 70% of participants who screen positive (target population) complete the baseline assessment.

• < 9% of parents of children in study classes^a to date participate in OSI

STOP:

• < 70% of participants who screen positive (target population) complete all assessments.

• < 9% of parents of children in study classes^a participate in OSI

Relevance and acceptability of all clinical and health economic outcome measures

• Proportion of missing data and patterns in missing responses/measures at baseline and follow-up assessments

• Descriptive statistics for clinical and health economic outcomes

• Qualitative interviews/discussion groups (children, parents/carers and school staff)

• Implement indicated changes to proposed outcome measures