This work concerns the professional development of UK teachers in their first year of teaching. It is interested in how the online discussions (ODs) these teachers undertook as part of the Master of Teaching contributed to this development process. The teachers worked in online tutor groups made up of teachers from different schools, phases (primary and secondary) and subjects. The data used were their accounts of participating in the ODs written towards the end of this first year of teaching and interviews with a selection of these teachers at a later stage in their career. It appeared that the learning gains of the ODs were enabled and fostered by writing for an audience of peers about their professional practice. These new teachers developed an inquiry-centred collegiality, reflexivity and a critical engagement with wider and longer-term educational perspectives. The research establishes that the gains from the ODs were the result of careful pedagogic design at many levels. By foregrounding the situated experiences and interests of the teachers, it allowed a "way in" for them to start to understand the complexities, dilemmas and strategies within their own and others' professional practice.