This study investigates the experiences of teachers in middle leading positions who worked as ESD facilitators during a three-year whole school approach project designed to implement education for sustainable development (ESD). Five schools in a Swedish municipality participated in the project to integrate ESD into their organisation and teaching practice. Project activities involved school leaders, teachers, and ESD facilitators, with the facilitators taking part in the design of the development process, workshop activities and content, and facilitating their school's internal work. The aim of this study is to generate insight into their roles as facilitators of transformation in line with ESD, and how they can be supported to fulfil their roles. The analysis used a framework of sustainability change agents, identifying that approaches to change aligned with technician, mediator, convincer, and concerned explorer types. The findings highlight the importance of contextual factors -- specifically, a shared vision, collaborative culture and organisational structures, and active school leadership in shaping ESD facilitators' ability to fulfil their roles.