This paper examines the development of e-learning mediating tool(s) for an online professional development programme, focusing on sustainability and teacher education, implemented across 11 countries in the southern African region. The paper focuses on how we approached the design and development of an online mediating tool(s) for interactive, situated learning that seeks to support sustainability practices and engagement of teacher educators at a local level while learning together with others across national borders. Using cultural historical activity theory, we elaborate on our understanding of mediation and then focus on the design and the development of the e-learning mediating tool, which we describe as an expansive learning process in our research and practice community. Our main finding is that to establish an interactive learning environment for situated, transformative learning in teacher education settings requires a comprehensive complex process of collaborative learning supported by a range of e-learning mediation tools, that are complemented by on-site engagement and support in communities of practice. We conclude that the successful deployment and use of an e-learning mediating tool depends on interconnected learning systems that is supported by the development of digital literacy skills, continuous online support, and similar communication tools.