Education policies across sub-Saharan Africa require teachers to change from being transmitters of knowledge to facilitators of learning. This means that teacher education needs to change as well and professional development which focuses on practical teaching is urgently needed. The Teacher Education for sub-Saharan Africa (TESSA) MOOC -- "Making teacher education relevant for 21st Century Africa" -- was designed to support teacher educators in changing their practice. The MOOC modelled socio-cultural theories of learning and focused on issues identified by the TESSA network. It ran four times, over two years, and nearly 9000 participants, mainly from sub-Saharan Africa (SSA), registered. For many it was their first experience of online learning. They studied on phones, in environments where electricity and connectivity were erratic, and supported each other in local communities. We draw on survey data from the first two presentations and in-depth interviews with four MOOC graduates to understand who took part, how they studied, what they learnt and how it has impacted on their practice and professional identity. For some individuals the experience was transformational. The study highlights the potential of this form of professional development, to make a difference particularly in a policy environment which is seeking pedagogic change.