Unraveling the "black box" of school tobacco policy implementation: A mixed-methods study at Danish vocational schools informed by Normalization Process Theory.

Background: Smoke-free policies are often poorly implemented in schools. The Smoke-Free Vocational Schools intervention aimed to support the routine implementation of a comprehensive school tobacco policy at Danish vocational schools and took place across seven schools. This study aimed to assess and understand the mechanisms-that is, reasoning and behavior change-that shaped if and how policy implementation outcomes occurred. Method: We applied a convergent mixed-methods design informed by Normalization Process Theory (NPT). The quantitative strand employed a repeated cross-sectional design, assessing implementation mechanisms-Coherence, Cognitive Participation, Collective Action, Reflexive Monitoring-and implementation outcomes at two time points: 5+ months post-policy (T1) and 14+ months post-policy (T2). Additional mechanisms-Change Commitment and Change Efficacy-were surveyed among subsamples who completed questionnaires pre-policy (T0) and at the follow-ups (i.e., T0-T1 and T0-T2). The qualitative strand involved interviews and focus groups with 40 participants to explore the mechanisms and their connections to intervention activities. Integration of qualitative and quantitative findings was achieved through joint displays. Results: Quantitative analyses included responses from N = 419 participants at T1, N = 452 at T2, N = 209 at T0-T1, and N = 182 at T0-T2. All implementation mechanisms were significantly and consistently associated with the total implementation outcomes score. Coherence encompassed the perceived meaningfulness of the policy, for example, believing the policy was a school responsibility. Cognitive Participation was related to policy legitimacy, for example, enforcement legitimacy beliefs. Collective Action involved practical implementation efforts, for example, enforcement and communication strategies. Reflexive Monitoring encompassed perceived policy impacts, for example, reduced smoking visibility. Change Commitment and Change Efficacy were found to be closely interrelated with the other mechanisms. Moreover, qualitative analysis revealed plausible connections between intervention activities and mechanisms. Conclusions: This study identified critical mechanisms for implementing school tobacco policies and demonstrated how specific intervention activities can activate these mechanisms, offering guidance for future research and practice development.