Purpose: This study aims to explore how the boundary between science and society can be addressed to support the transformation of higher education towards sustainable development (HESD) in the sense of the whole institution approach. It analyses students' learning experiences in self-led sustainability projects conducted outside formal curricula to highlight their potential contribution to HESD. The students' projects are conceived as learning spaces in "sustainability-oriented ecologies of learning" (Wals, 2020) in which five learning dimensions can be examined. Design/methodology/approach: Using an iterative, grounded-theory-inspired qualitative approach and sensitising concepts, 13 in-depth semi-structured interviews were conducted exploring students' learning experiences. Interviews were categorised in MAXQDA and analysed against a literature review. Findings: Results revealed that students' experiences of non-formal learning in self-led projects triggered deep learning and change agency. Trust, social cohesion, empowerment and self-efficacy were both results and conditions of learning. Students' learnings are classified according to higher education institutions' (HEIs) sustainability agendas, providing systematised insights for HEIs regarding their accommodative, reformative or transformative (Sterling, 2021) path to sustainable development. Originality/value: The education for sustainable development (ESD) debate focuses mainly on ESD competences in formal settings. Few studies explore students' learnings where formal and non-formal learning meet. This article investigates a space where students interact with different actors from society while remaining rooted in their HEIs. When acting as "change agents" in this hybrid context, students can also become "boundary agents" helping their HEIs move the sustainability agenda forward towards a whole institution approach. Learning from students' learnings is thus proposed as a lever for transformation.