School Gardening and Health and Well-Being of School-Aged Children: A Realist Synthesis

School environments can create healthy settings to foster children’s health and well-being. School gardening is gaining popularity as an intervention for healthier eating and increased physical activity. We used a systematic realist approach to investigate how school gardens improve health and well-being outcomes for school-aged children, why, and in what circumstances. The context and mechanisms of the specific school gardening interventions (n = 24) leading to positive health and well-being outcomes for school-aged children were assessed. The impetus of many interventions was to increase fruit and vegetable intake and address the prevention of childhood obesity. Most interventions were conducted at primary schools with participating children in Grades 2 through 6. Types of positive outcomes included increased fruit and vegetable consumption, dietary fiber and vitamins A and C, improved body mass index, and improved well-being of children. Key mechanisms included embedding nutrition-based and garden-based education in the curriculum; experiential learning opportunities; family engagement and participation; authority figure engagement; cultural context; use of multi-prong approaches; and reinforcement of activities during implementation. This review shows that a combination of mechanisms works mutually through school gardening programs leading to improved health and well-being outcomes for school-aged children.


Introduction
Access to and consumption of healthy, nutritious food plays a crucially important role in maintaining good health and well-being and is a fundamental human right [1,2]. For many populations worldwide, however, deep-rooted and complex underlying problems associated with food systems influence the availability and access to healthy diets and nutritious food [2]. Food security exists when all people, at all times, have physical, social, and economic access to sufficient, safe, and nutritious food that meets both their dietary needs and food preferences for an active and healthy life [3]. Unfortunately, these conditions remain elusive for many [4], and in some instances, this leads to food insecurity. According to the Food and Agriculture Organization of the United Nations (FAO), the ability to be food secure largely depends on the uninterrupted supply and availability of different types of healthy food, food utilization, and the stability of each of these dimensions over time [3]. Additionally, a range of social determinants underpins the inequities in healthy eating [5]. For example, 'urban poverty', resulting from lower income availability, may lead to inadequate resources for people affected by such circumstances in accessing healthy

Context-Mechanism-Outcome Configuration
For each intervention identified, a Context-Mechanism-Outcome configuration was developed, using the extracted data together with supplementary information from the TIDier process (Table 1).

Context-Mechanism-Outcome Configuration
For each intervention identified, a Context-Mechanism-Outcome configuration was developed, using the extracted data together with supplementary information from the TIDier process (Table 1).

Context (Materials/Activities) Mechanism Outcomes (Health/Well-Being)
How do you grow? How does your garden grow? [25,26] 10-week program with Grade 5-6 students • "How do you grow?" nutrition education curriculum with topics on body, plants, nutrition, health, physical activity, and goal setting • "How does your garden grow?" school garden component included the use of a garden and the production of a classroom cookbook • Newsletters to encourage fruit and vegetable intake by families  [52] 1-year program with Grade 4-5 students • Curriculum comprised of five components: nutrition education and promotion, family and community partnerships, supporting regional agriculture, school food availability, and school wellness • Activities included nutrition education, cooking demonstrations, school gardens, family newsletters, health fairs, salad bar implementation, procurement of regional produce, and school wellness committees • Compared with students exposed to less than two intervention components, students who were exposed to two or more components scored significantly higher on fruit and vegetable intake, self-efficacy, and knowledge and lower on preference for unhealthy foods • Although not significant, farmer's visits, taste testing, and cafeteria components had the largest effect sizes
Some interventions were adapted from existing curricula, activity guides, peer-reviewed resources, or garnered from previous pilot initiatives. For example, several interventions were based on the curriculum of Junior Master Gardener ® (College Station, TX, USA) and Health & Nutrition from the Garden programs [37,43,54], and several utilized the activity guide developed by Lineberger and Zajicek (1998) [25,26,50,51]. Further, a few interventions were based on the model of Montessori (1964) and grounded in school gardening research and garden-based learning [49,57].
The reinforcement of activities leading to sustainability was also seen as a key mechanism, such as repeated and/or increased exposure to fruit and vegetables during the intervention duration. The notion of ensuring the impacts of school gardening activities was sustained was also accomplished by consistent and coordinated messaging through multiple intervention components [36,37,39,40,43,52].

Discussion
Through this realist synthesis, we investigated how school gardening improves health and well-being for school-aged children, finding that a combination of mechanisms operates in tandem under different contexts for the success of the school gardening interventions to yield positive outcomes. The impetus of many interventions was to increase fruit and vegetable intake and address the prevention of childhood obesity. Most were conducted at primary schools with participating children in Grades 2 through 6 and were located in high-income countries, including the United States and Australia. The mechanisms ranged from embedding nutrition and garden education in the curriculum to experiential learning, engagement and involvement of family and "authority figures", and the relevance of cultural context. Types of positive outcomes included increased fruit and vegetable consumption, dietary fiber and vitamins A and C, improved BMI, and improved well-being of children.
The review results in evidence that the benefits of combining nutrition-based and garden-based education are important in improving outcomes, particularly with attitudes and behaviors toward fruit and vegetable consumption. This suggests that classroombased lessons may be enhanced through practical and garden-based lessons. For example, in the How do you grow? How does your garden grow? intervention, the curriculum encompassed a variety of topics in relation to health and well-being, reinforced through 'hands-on' exposure to gardening activities [25,26]. Similarly, the Nutrition in the Garden program integrated nutrition education into the curriculum, with particular emphasis on a practical application involving comprehensive gardening and cooking activities [50,51]. In addition, findings from Berezowitz et al. (2015), through a review of school garden studies, conclude that garden-based learning may favorably affect fruit and vegetable consumption but also positively impacts academic performance [11]. Similarly, experiential learning strategies have proved useful in improving children's knowledge, attitudes, and behaviors toward eating more healthily, including those in school garden settings [18]. Schools, therefore, have significant potential to create garden spaces for enabling experi-ential experiences linked to the curriculum, leading to enhanced learning and improved health and well-being outcomes.
Family involvement in school gardening initiatives was at the center of impacting positive health and well-being outcomes, demonstrated across several interventions, with mechanisms working at multiple levels. Previous research reports that family involvement helps change eating behaviors in school-aged children [14]. Consistent with the "bioecological theory" and "primary socialization theory", a child's development is collectively impacted by numerous proximal (e.g., parents, peers, community) and distal (e.g., cultural norms, laws, customs) influences and their complex interdependencies [60]. Accordingly, the importance of parents in promulgating healthy nutrition behaviors in children cannot be underestimated. Garnering the cooperation/participation of as many parents as possible in school-based gardening can be strengthened using volunteering programs and take-home activities, including produce and recipes. These strategies have proven to be effective at meaningfully engaging parents with school-garden-related activities [14].
Visionary leadership and inspirational role models are integral to school-based gardening interventions leading to health and well-being outcomes. Strong engagement between students and "authority figures", including school teachers, school principals, and external experts, has consistently been shown to be associated with positive health and well-being outcomes. For example, Growing Schools and The Gloucestershire Food Strategy identified clear leadership and vision from the head teacher as critical for initiating change [33]. Findings from the Royal Horticultural Society Campaign for School Gardening indicate how the willingness of teachers to engage with the intervention may be important towards a greater intake of fruit and vegetables [35]. In addition, Viola (2006) identified how support from the school principal is key in the Outreach School Garden Project, leading to improved nutrition knowledge and skills [28]. More recently, Mann et al. (2022) synthesized evidence of nature-specific outdoor learning outside of the classroom on school children's learning and development and suggested that all teacher training efforts should include skill development activities pertaining to this type of pedagogical approach [61]. Integration of ideas such as these is important as teachers are often highly influential during childhood education and development, as indicated above.
Considering the increasingly diverse societies we dwell in, it is no surprise that many made a conscious effort to accommodate the varying cultural needs in their interventions. For instance, culturally-tailored components, together with experiential learning, were central to the LA Sprouts program, leading to many potentially beneficial outcomes, including changed behaviors and preferences towards dietary fiber, fruit, and vegetables for children of Hispanic/Latino heritage [44][45][46][47][48]. Similarly, Ornelas and colleagues (2021) reported the importance of drawing on cultural strengths and traditional practices in addressing childhood obesity through school gardening, specifically for American Indian communities [62]. Therefore, cultural aspects and/or ethnic diversity would be an important consideration in the design of school gardening programs to ensure potential health and well-being outcomes are culturally sensitive and sustainable.
This realist review highlights that several key elements and numerous permutations of context and mechanisms work mutually, leading to positive health and well-being outcomes in school-aged children that may be observed collectively ( Figure 2; Table 1). The synthesis demonstrates the potential for change when important contextual and mechanistic elements are drawn from a range of successful interventions that may be incorporated into current or proposed school gardening programs. This provides guidance in conjunction with published systematic and meta-analysis reporting on school gardening interventions. This also provides a template for consideration in designing new school gardening interventions or enabling adjustment and inclusion of additional elements to current interventions. synthesis demonstrates the potential for change when important contextual and mechanistic elements are drawn from a range of successful interventions that may be incorporated into current or proposed school gardening programs. This provides guidance in conjunction with published systematic and meta-analysis reporting on school gardening interventions. This also provides a template for consideration in designing new school gardening interventions or enabling adjustment and inclusion of additional elements to current interventions. To the best of our knowledge, this is the first time a systematic realist synthesis with the accompanying use of program theory has been applied to school gardening interventions. The strength of this approach lies in using high-level research-based evidence through the identification of systematic and meta-analysis reviews. This informed identification of pertinent peer-reviewed primary articles with positive health and well-being outcomes and subsequent identification of school gardening interventions. This approach enabled the identification of evidence associated with school-based gardening interventions as previously identified and reviewed, allowing a comparison of our findings with the existing literature. Data extraction and TIDier checklist methodologies enabled holistic assessment of individual school gardening interventions, supporting robust configuration of context, mechanism, and outcomes and subsequent realist synthesis.
Notwithstanding the potential for positive outcomes that result from school gardens, it is important to note that the generalizability of the results from these interventions may be limited to high-income countries as most of the programs were based in Australia, the United Kingdom, and America. In addition, while a number of programs were based in areas of socio-economic disadvantage, addressing particular health inequities affecting low-income, under-resourced, and/or specific ethnic groups, including a focus on To the best of our knowledge, this is the first time a systematic realist synthesis with the accompanying use of program theory has been applied to school gardening interventions. The strength of this approach lies in using high-level research-based evidence through the identification of systematic and meta-analysis reviews. This informed identification of pertinent peer-reviewed primary articles with positive health and well-being outcomes and subsequent identification of school gardening interventions. This approach enabled the identification of evidence associated with school-based gardening interventions as previously identified and reviewed, allowing a comparison of our findings with the existing literature. Data extraction and TIDier checklist methodologies enabled holistic assessment of individual school gardening interventions, supporting robust configuration of context, mechanism, and outcomes and subsequent realist synthesis.
Notwithstanding the potential for positive outcomes that result from school gardens, it is important to note that the generalizability of the results from these interventions may be limited to high-income countries as most of the programs were based in Australia, the United Kingdom, and America. In addition, while a number of programs were based in areas of socio-economic disadvantage, addressing particular health inequities affecting lowincome, under-resourced, and/or specific ethnic groups, including a focus on childhood obesity prevention, the results may not be entirely generalizable and transferable to other settings, either in other high-income countries or low-income countries.

Conclusions
Through this realist synthesis of identified school gardening interventions, we have shown how various mechanism work mutually to support positive health and well-being outcomes of school-aged children in particular contexts, which may assist with future endeavors. School gardening interventions potentially hold strong promise in supporting action toward the prevention of modern public health problems, including food insecurity and childhood obesity, both requiring urgent global attention.