As on-line discussion becomes an increasingly important and significant aspect of teachers' professional education, most particularly as part of distance learning environments, there is a need to understand and develop effective analytic techniques that provide insights into the processes at work within these systems. In this study investigates knowledge construction in online dialogue in a post graduate course. This involves looking at situations in which there is an introduced topic focus and also in alternative online forums where there is not a clearly defined shared task and participation is voluntary. This paper reports on work in progress building on previous studies of tools of analysis of online conferences (Cook and Ralston 2001). It will examine what effect the introduced discussion topics have, if any, on the pattern of involvement by making comparisons between contexts in which there are interventions and others where there are none.