Preventing smoking initiation among vulnerable adolescents: a process evaluation of the KickAsh!-intervention in Flemish youth social work settings

Background Smoking disparities remain a global concern, with adolescents experiencing societal vulnerability at increased risk of cigarette smoking initiation. Persistent inequities suggest that prevention interventions often fail to engage these adolescents, partly because they insufficiently reflect their everyday environments and social contexts. Although schools are commonly used settings, their impact is often limited for this group, underscoring the need for more context-sensitive approaches and to explore complementary settings. To address this, the KickAsh!-intervention was co-created with adolescents and youth workers within youth social work organisations. In an accompanying paper, the effectiveness study of KickAsh! showed no significant effects, highlighting the need to examine how the intervention was implemented in practice. This study therefore presents a process evaluation, aiming to understand the mechanisms underlying its (lack of) effects and how implementation interacts with context in real-world settings. Methods KickAsh! was implemented across eight youth social work organisations. Qualitative data were collected through seven focus groups with adolescents ( n = 52) and eight interviews with youth workers ( n = 8). Framework analysis enabled systematic organisation of data, cross-case comparison, and identification of deeper themes. Results Seven themes emerged: (1) perceptions of the intervention and its impact, (2) preferences and the importance of adaptability, (3) influence of youth workers’ smoking status, (4) influence of their skills and motivation, (5) organisational structure and context, (6) addressing smoking within youth social work, and (7) participation and co-creation. Conclusion Implementation of the KickAsh!-intervention varied substantially across youth social work organisations due to interacting individual, organisational, and intervention-related factors, highlighting its strong context dependency. This variability may explain the limited observed effects, although the intervention appeared to foster important unmeasured outcomes such as awareness, open dialogue, and organisational capacity. The development and refinement of a theory of change further underscored that inconsistent implementation and limited fidelity were key drivers of these findings, alongside broader contextual influences. Youth workers played a pivotal role, as their characteristics, skills, and capacity largely determined success. Embedding flexibility to adapt the intervention to each organisation’s specific context and needs appears crucial for feasibility, impact, and sustainability. Trail registration This study is part of a larger project that includes the development, implementation and evaluation of the KickAsh! - intervention. The study protocol of this project is registered on ClinicalTrials.gov (NCT05920772).