Mechanisms for scale-up: Case example of a school-based mental health approach in the Netherlands

• This study provides insight into how STORM, a school-based mental health approach, was implemented on a large scale in the Netherlands. • Large-scale implementation of STORM was achieved through three mechanisms: (A) raising mental health of adolescents as a policy problem, (B) promoting STORM as a potential solution for this problem, and (C) influencing politics to improve the uptake of STORM. • Dedication and credibility of the core STORM team and a sense of ownership among stakeholders were important determinants contributing to all three mechanisms. • The application strategies to disseminate STORM, to organise and finance scale-up, and to evaluate the scale-up process contributed to all three mechanisms. : The prevalence of mental health problems in adolescents is high. Effective scale‑up of school‑based approaches is crucial for improving youth mental health, yet well‑documented examples remain scarce. This study examined the scale‑up of the school‑based preventive mental health approach STORM (Strong Teens and Resilient Minds) between 2011 and 2025 to identify mechanisms that enabled its sustained expansion. : A qualitative case study was conducted using in‑depth interviews with 30 stakeholders involved in the STORM scale‑up over time, including researchers, policy officials, and managers and professionals in education and youth (mental) healthcare. The Multiple Streams Framework guided data collection and analysis. Thematic analysis was applied, and findings were verified with participants. Three mechanisms shaped scale‑up decisions: (A) rising societal awareness of adolescent mental health problems and suicidality as urgent public health concerns; (B) strategic positioning of STORM as a feasible, evidence‑informed policy solution for schools; and (C) cultivation of a supportive political climate for adoption at regional and national levels. Across these mechanisms, the credibility and long‑term commitment of the core STORM team, stakeholders’ sense of ownership, and consistent strategies for dissemination, organization, financing, and evaluation were central to successful scale‑up. : This study demonstrates how contextual developments and deliberate strategic actions jointly facilitated the expansion of a school‑based youth mental health approach. The findings offer actionable insights for researchers, policymakers, and practitioners aiming to scale up mental health promotion and prevention initiatives for young people.