Using the behaviour change intervention ontology to examine the inclusion, delivery and experience of behaviour change techniques in a youth health promotion programme.

Adolescents from low socioeconomic backgrounds face disproportionate risks to health and well-being, underscoring the need for targeted, evidence-based interventions. Systematic extraction of active ingredients in interventions can inform the design of more effective interventions. This study aims to (1) identify Behaviour Change Techniques (BCTs) and Mechanisms of Actions (MoAs) used to change behaviour in the '11 for Health' programme, (2) interview programme receivers and deliverers exploring their experiences with BCTs and MoAs. Twenty-four BCTs were coded in the manual with 10 associated MoAs. Thematic analysis of interviews generated 16 codes for adolescents and 17 for teachers, each mapped onto BCTs. Adolescents highlighted, 'social support' and 'agree outcome goal', while teachers emphasised 'social support' and 'information about health consequences'. Further research is needed to substantiate whether potential refinements to the programme and inclusion of new BCTs, as identified in the interviews, could lead to enhanced effectiveness and long-term impact of the programme.Trial registration: This is a secondary analysis of a clinical trial, which has been registered at: ClinicalTrials.gov ID: NCT03647007.