IMplementation and evaluation of the school-based family support PRogram a Healthy School Start to promote child health and prevent OVErweight and obesity (IMPROVE) – study protocol for a cluster-randomized trial

BACKGROUND: IMPROVE aims to conduct a hybrid type 3 evaluation design to test the effectiveness of bundled implementation strategies on intervention fidelity of the Healthy School Start (HSS) program, while simultaneously monitoring effects on health outcomes of children and parents. The HSS is a 4-component family support program for children starting school (5–7 years of age) promoting healthy dietary habits and physical activity in the home environment to prevent childhood obesity and parents’ risk of developing type 2 diabetes. METHODS: IMPROVE is a cluster-randomized controlled trial with two arms to evaluate and compare the effects of two different bundles of implementation strategies on intervention fidelity expressed as adherence and responsiveness at 12 and 24 months (primary outcomes). Thirty schools in two municipalities will participate in the study reaching about 1400 families per school year. In stakeholder workshops, key implementation determinants were identified according to the domains of the Consolidated Framework for Implementation Research. Through a consensus process with stakeholders, two bundles of implementation strategies were tailored to address context-specific determinants. Schools randomly assigned to group 1 will receive bundle 1 (Basic) and group 2 will receive bundle 1 + 2 (Enhanced). Bundle 2 consists of external facilitation, fidelity monitoring and feedback strategies. Secondary outcomes will include change in acceptability, appropriateness, feasibility, and organisational readiness as perceived by school staff. In addition, child weight status and diet, and parents’ feeding practices and risk of type 2 diabetes will be monitored. Linear and ordinal regression analysis will be used to test the effect on the primary and secondary outcomes, taking clustering and covariates into consideration where needed. Process evaluation will be conducted through key stakeholder interviews to investigate experiences of the program and perceptions on sustainability. DISCUSSION: This systematic approach to investigating the effectiveness of two different bundles of implementation strategies tailored to context-specific determinants on the fidelity of the HSS intervention will provide new insight into feasible implementation strategies and external support needed for the HSS to be effective and sustainable. Results will help inform how to bridge the gap between the research on school-based health programs and routine practice in schools. TRIAL REGISTRATION: Registered prospectively at ClinicalTrials.gov ID: NCT04984421, registered July 30, 2021 SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-021-11663-2.