Teachers are expected to implement new educational technologies and adapt to new teaching environments. However, it involves a complex learning process that can lead to their perspective transformation. We have developed and taught a discussion-based online course to facilitate teachers' transformative learning. This qualitative case study examines teachers' perspective transformation in our course to understand the nature of effective online teacher-to-teacher discussions. Based on a theoretical framework that integrates Mezirow's transformative learning model and Bakhtin's dialogism, this paper builds on previous literature on teacher-to-teacher discussions as well as providing a fresh perspective to inform the current globalized teacher education context.