Background/Aims -
With complex problems relating to climate change and human health shaping society in the twenty-first century, the ability of schools to foster awareness and proactive behaviours around these issues is of pressing concern to public health practitioners, educators, and policymakers. This exploratory and iterative thesis maps what is known about the extent and range of integrated health and sustainability approaches undertaken in schools globally. It explores why schools have acted around these issues and how.

Methods -
A mixed-methods research approach makes use of current evidence to inform effective and responsive further inquiries. The thesis consists of three empirical research studies that were designed and undertaken sequentially, as follows:
1. Systematic scoping review of global evidence (Chapter 3)
2. Thematic synthesis of global evidence (Chapter 4)
3. In-depth qualitative case study of New Zealand Enviroschools
(Chapters 5 and 6)

Findings -
The systematic scoping review of global evidence collated 87 sources. The four main areas in which integrated approaches were implemented were: teaching and learning (n= 27), physical environment adaptations (n= 23), ecologically focused policy development (n= 13) and whole-school holistic approaches (n= 12). Evidence has increased in the last two decades and is heterogeneous in nature, with few sustained attempts to explain the potential role of theory in design, implementation, and evaluation of healthy green approaches.
The thematic synthesis generated four key drivers of integrated approaches: an awareness of the urgency of issues related to the environment and human health; a need for systemic solutions to wicked problems; increased levels of reflective curiosity; and a focus on transformative actions. Across the evidence, integrated approaches were thought to foster connected systems (between upstream and downstream school influences) and connected thinking (through action-oriented, place-based experiences). The evidence suggests that holistic approaches that seek to reorient whole-school culture through action and policy are deemed most likely to reflect the urgency and systemic nature of the climate emergency. Across disciplines, three theories resonate with integrated school-based action and policy: (eco)sociological theories (education), transformation theories (social science), and salutogenesis (public health).
The in-depth qualitative case study of New Zealand ‘Enviroschools’ reveals the importance of quality relationships with others, environments, and oneself in the design, implementation, and sustainability of an approach that aims to foster healthier and more environmentally aware young people within the mainstream school context. Implementation strategies such as planning using a sustainability lens, co-ordination between regional and national networks, and providing those involved with feedback in context, were associated with building and nurturing quality relationships across the school community by encouraging connections and a shift in mindset around change.

Implications -
The findings generated in this thesis outline why a mainstream movement towards an integrated conceptual ‘third space’ may be necessary at the intersection between health, environment, and education. This ‘third space’ refers to an integration of health (first space) and environment (second space) into a socioecological (third space) that is united in its complexity rather than divided into separate complex problems. A movement towards an integrated conceptual ‘third space’ may connect previously disaggregated systems and thinking to reveal transformative and pragmatic ways in which schools can develop, implement, and sustain action and policy which nurtures healthier and more environmentally aware young people.