Abstract
BACKGROUND: The Engaging Adolescents in Changing Behaviour trial tested the impact of an adolescent diet and physical activity intervention involving: teacher training in Healthy Conversation Skills, a health education module (LifeLab) and a gamified smartphone application ('the app'). The process evaluation described in this paper examined the implementation, context and mechanisms of impact of the intervention (the core elements of the Medical Research Council guidance on process evaluation of complex interventions), to identify how and why participants did or did not engage with each element of the trial and the intervention. METHODS: A mixed-methods approach was employed. 51 interviews with students, teachers and parents from 11 secondary schools were conducted and analysed using thematic analysis. Quantitative data reported numbers of students who attended LifeLab and downloaded and used the app. RESULTS: 87.9% of eligible students attended LifeLab and 45.7% of eligible students downloaded the app. Students (n=72) and teachers (n=16) had positive experiences of LifeLab and the teacher training, despite the pandemic preventing in-person delivery for some schools. Students engaged in a limited way with the app. Parents (n=11) had positive views of the research but little knowledge of the intervention. Students valued learning about their own health, and teachers were enthusiastic about supporting their students' health but struggled to find opportunities to do so. CONCLUSIONS: Schools are appropriate settings in which to implement health interventions, but the research must benefit teachers and students. Most students did not engage with the app because they were not presented with it in a way that motivated them to use it. Careful consideration of the design of apps is required to encourage students to use them. Parents should be involved in research in ways that are accessible to them.