While few studies have captured primary school learners’ understandings of sustainability education, there is a lack of co-research with learners on how they recognise and interpret their lived sustainability education experiences in relation to their school’s specific approach. This thesis has explored pupils’ reflective accounts of their sustainability education experiences through reflexive and design-led approaches, as part of a designed co-researcher engagement. Involving two small primary schools in Scotland and New Zealand as case studies, the participatory and collaborative research aimed to raise learners’ awareness of their existing sustainability education in their everyday schooling. Responsive to exploring how sustainability education is embedded in schools, walking interviews with teachers invited place-based reflections on existing pedagogical practices. Additionally, interviews with education stakeholders from across the public and third sectors were undertaken to reveal surrounding policy and contextual challenges. These practitioner perspectives contextualised each pupil’s place-responsive and time-bound sensemaking. Methodologically, the diary method, complemented by creative engagement with learners, cultivated an interplay between reflexive and dialogic, private and shared, as well as individual and collective co-research spaces. These were vital for a transformative learning experience to emerge in the field as learners reflected on their personal opinions, values and understandings of the somewhat abstract topics of climate change, sustainability and education. Creatively co-researching with learners through diary methods, creative dialogues, letter-writing, and visual mapping, the findings reveal insights into 8-to-12-year-olds’ strong sense of place and belonging towards the school grounds, community and lived institutional culture around sustainability. With the research based in schools that are already highly engaged with learning for sustainability, and mirrored in learners’ creative work, the findings illustrate how their experiences are grounded in schools’ context-specific, place-responsive and relational approaches to sustainability. Learners did not explicitly refer to knowledge gained from subject lessons but identified sustainability-oriented learning in the informal times, places and encounters in-between classes. Thus, the learner-centred Participatory Action Research nuances current understandings of how young learners experience a school’s sustainability-oriented engagement within and beyond the curriculum, specifically in contexts of more climate-supportive education policies in Scotland and New Zealand. Practitioners’ reflections importantly acknowledge the persistent challenges that continue in practice despite a shared school’s commitment towards prioritising a holistic embedding of sustainability education. Its impact on learners, however, as found in this study, emphasises what can be learned from learners' subjective and tacit knowing of sustainability education in school-specific contexts. As for considering whole-school approaches through a community of practice lens, implications are derived from the often-hidden impact on pupils’ learning experiences at the informal times, in places and encounters in-between lessons and beyond, as this is how, when, with whom and where learners see sustainability education enacted as learning in the in-between - every day.