UK adolescents’ nutritional intakes are currently suboptimal⁽¹⁾, and thus, effective and sustainable dietary interventions are urgently needed to improve health outcomes among this population. School-based, student-led initiatives have been proposed as a suitable approach to aid in improving adolescents’ dietary behaviours^{(Reference Devine, Gallagher and Hill2)}, albeit, evidence of such strategies remains limited. To address this, a peer-led pilot feasibility intervention was designed and implemented in the post-primary school-setting to encourage adolescents to improve their dietary choices in the school canteen at lunchtime. The aim of this study was to qualitatively assess the acceptability of this intervention among participating pupils, peer-leaders and school staff.

The peer-led intervention was a 12-week pilot feasibility cluster-randomised controlled trial, targeting Year 8 pupils who had transitioned to the first year of post-primary school. A convenience sample of four post-primary schools (n = 3 intervention; n = 1 control) in Northern Ireland (NI) were recruited and Year 8 pupils (aged 11–12 yrs) and Year 13 peer-leaders (aged 16–17 yrs) were invited to participate. In the intervention schools, peer-leaders were trained to assist with the design, implementation, and monitoring of various intervention components across the 12-week intervention period. Selected intervention components (e.g. labelling strategies, menu displays, placement manipulations and reward schemes) were guided by previous work conducted with NI school staff^{(Reference Devine, Gallagher and Hill2)} and pupils^{(Reference Devine, Gallagher and Hill3)}. Following completion of the intervention, semi-structured one-to-one interviews with school staff (n = 6) and focus groups with Year 8 pupils (n = 21) and Year 13 peer-leaders (n = 28) were conducted between April to May 2022 to explore the acceptability of the intervention from a range of stakeholder perspectives. Discussions were audio-recorded and transcribed verbatim. All transcripts were imported to NVivo12 software for data management and analysed thematically using a deductive and inductive approach^{(Reference Braun and Clarke4)}.

Six overarching themes were generated from the discussions, namely: intervention acceptability (perceptions of intervention components, level of enjoyment, intervention strengths, willingness to participate in the future); participation rates (rationale for participation); intervention effectiveness (perceived impact on dietary choices); intervention challenges (recruitment barriers, implementation barriers); intervention sustainability (short- term, long-term), and suggestions for improvement (strategies to overcome intervention barriers, general recommendations to improve the study).

Findings confirm that this peer-led intervention was feasible and the intervention components were acceptable among this population, with participants citing interest to take part if the study were to be conducted again. This study also highlighted several barriers to intervention implementation, for example, canteen supply issues, resulting in menus and labels not aligning with unanticipated food items served, limited capacity in the canteen environment, peer-leaders' academic commitments overlapping with pupils lunch period and pupils' inability to retrieve rewards due to misplacing their reward cards. Identified barriers should be taken into consideration by researchers in the design of future, larger-scale dietary interventions in the post-primary school-setting to optimise outcomes.