This paper introduces a rationale for change in roles and practices of the participants in mathematics education MA courses and their instructor, based on the integration and use of a web log, both as a medium for asynchronous communication, and as a mechanism for provoking professional reflection, through changes in the discursive style and the social practices of participants. It reports research carried out with 48 mathematics teachers, as students of two six-month academic (MA) courses. A framework for research and practice in on line learning (Garrison & Anderson, 2003) is related to theoretical constructs from the fields of mathematics education and online learning and is used as a first analytical filter. In terms of identifying kinds of discourse, the analytical categories used have aided in clarifying specific patterns. The first seems to be that of the development of different writing genres and the informal discursive style embedded in teachers' narratives. The second is the effort of participants to engage in communicatively demanding situations, adopting different roles and behaviours. These roles and behaviours are summarised in three profiles: the "blog enthusiast", the "blog frequent visitor" and the "blog sceptic".