Background: A ‘health promoting school’ approach has become an increasingly popular framework internationally within which to address the health needs of school communities. A growing evidence base indicates that, if applied successfully, a health promoting school approach can lead to improvements in both health and educational outcomes (including children’s psychological health and well-being). The Healthy Schools Programme (HSP) is an initiative developed through partnership between a Dublin-based voluntary sector organisation and a number of local urban DEIS band 1 schools, the aim of which is to promote positive health outcomes for children in their primary school years and including the psychological health and well-being of children (in line with health promoting principles). To date, few studies have comprehensively examined how such initiatives address the psychological health needs of children. Objectives: The overarching aim of this study was to examine how, and to what extent, the Healthy Schools Programme addressed the psychological health and well-being needs of a sample of primary school-aged children. The study assessed the impact of the initiative on children’s health outcomes including a focus on how the programme helped the schools to address psychological health. A secondary aim of the study was to explore the impact the implementation strategy on the overall effectiveness of the HSP. Method: A concurrent mixed methods design was used to address the study objectives. The study comprised two parallel phases: (1) a comparative impact evaluation of the HSP on children’s psychological health (aged 7-12 years) and; (2) a process evaluation of programme planning and implementation. Data were collected over a 24-month period using a number of methods including: (a) follow-up self-report health questionnaires with children (n = 434); and (b) one-to-one interviews and focus groups with key stakeholders (n=48) (i.e. HSP funders, Healthy Schools coordinators, school principals and staff, parents as well as health and educational professionals); and (c) non- participatory participant observation at steering committee meetings (n=9). The quantitative data were subjected to a series of descriptive and inferential statistical analyses including t-test, chi square, and ANOVA. Qualitative data were analysed thematically using Framework Analysis. Results: At baseline, children maintained average levels of psychological well-being as well as other aspects of health-related quality of life (e.g. physical well-being, peers and social support, autonomy and parental relations, school environment) relative to national and international studies. At follow-up, comparisons of self-report health measures between children in Intervention (n=5) and Comparison schools (n=2) found some health improvements for the entire sample over time. However, the lack of any substantial differences between Comparison and Intervention school samples suggest that any changes in health cannot be attributed to the HSP. The qualitative findings suggest some positive changes in how schools addressed health as a result of the HSP, although these were not demonstrated in the children’s health outcome data at the year 2 follow-up. The results of the process evaluation highlighted the slow, evolving and often challenging aspects of programme implementation. In particular, psychological health was not addressed by the HSP until the second half of the implementation period, and when prioritised, was identified by most participants as more challenging and complex than other aspects of health (i.e. nutrition and physical activity). A number of fundamental implementation factors were identified as not being sufficiently well developed to facilitate the effective implementation of the HSP in the local context. These included: a lack of a shared understanding of the HSP amongst all key stakeholders (including the planning group); an absence of appropriately experienced Healthy Schools Coordinators; poorly developed forms of collaboration and joined-up working; and the lack of a properly functioning national health promoting school framework/governmental support. It was evident that more coherent planning and a retrospective process of review (relating in particular to the quality of the HS manual and issues around implementation fidelity) were needed for more effective programme implementation. Conclusions: This study provided a comprehensive assessment of how a local health promoting school initiative attempted to address the psychological health and well-being of children in an Irish primary school setting. Importantly, the study also examined the process of programme implementation as well as the impact of the programme on children’s psychological health. The study findings clearly demonstrate the complexity and many challenges involved in developing and implementing a HSP initiative in an Irish context and also in using this approach to tackle the psychological/mental health needs of school children. The identification, in this study, of key enablers of, and barriers to, the implementation of the local health promoting school initiative is important in informing the design, planning and implementation of these kinds of initiatives both in Ireland and elsewhere.