Table 1.

Process evaluation domains and research questions

Process evaluation domain	Research question
Mechanisms of change	RQ1: Are the intervention’s mechanisms of change operationalised as hypothesised? RQ2: How is the operationalisation of the mechanisms of change influenced by contextual factors? RQ3: Does the interaction of the mechanisms of change with contextual factors give rise to unintended effects?
Programme differentiation and usual practice	RQ4: Is the Wellbeing in Secondary Education (WISE) intervention differentiable from ‘usual practice’ and does this differentiation change during the study? RQ5: Is there contamination of usual practice in control schools by receipt of the WISE intervention or similar approaches?
Implementation (WISE training components)	RQ6: What is the reach of the WISE training components (e.g. 8% of staff attending Standard Mental Health First Aid)? RQ7: How many targeted staff complete the WISE intervention training? RQ8: Are the WISE training components delivered with fidelity and what is the nature of any adaptions undertaken? RQ9: Are there differences in the delivery of the WISE training components between England and Wales, and what gives rise to any differences? RQ10: How well are the WISE training components delivered?
Implementation (peer support service)	RQ11: What proportion of teachers receive support from the peer support service? RQ12: Is the peer support service delivered with fidelity and what is the nature of any adaptions undertaken? RQ13: What are the barriers and facilitators to the implementation of the peer support service?
Acceptability	RQ14: Is the WISE intervention acceptable to funding organisations, intervention trainers, head-teachers, teachers and students?
Sustainability	RQ15: How likely is the WISE intervention to be sustainable and what factors might ensure sustainability?