This study investigates the experiences of teachers working as ESD-facilitators in a whole school approach project designed to implement education for sustainable development (ESD). The project included ESD-facilitators, teachers, and school leaders. The ESD-facilitators took part in designing joint seminars and workshop activities, and facilitated each school’s internal work. This study aims to contribute with knowledge concerning in what ways ESD-facilitators function as change agents in development processes and how their work can be supported. Different types of sustainability change agents who position themselves differently along the two dimensions of personal detachment vs. personal involvement, and instrumental vs. open-ended approaches (to change and learning) have been identified in previous research (Van Poeck et al., 2017). This study investigates the views and practices of ESD-facilitators in relation to these two dimensions, and focuses on what sustainability change agent functions are enacted, and what contextual factors they experience as successful and/or hindering in their work. Data were collected through semi-structured interviews with seven ESD-facilitators from five schools. Focus areas were their views on: a) the long term goals of the project, b) their role in the internal development work, and c) factors of central importance for their ability to perform their task effectively. The findings indicate that roles and processes become more open-ended in schools where there is room for collaborative and reflexive work. In schools where the culture encourages shared agency, the ESD-facilitators point to their functions in mediating the process in terms of mobilizer, facilitator, initiator, and/or awareness raiser (Ibid.). When there is little room for collaborative work, or the culture impedes it, the ESD-facilitator role and approach become more instrumental and it is harder to integrate ESD and create agency. Those facilitators emphasized their functions in terms of managers, solution providers, experts, exemplars and councellors (Ibid.).