This article explores some specific issues involved in online learning and assessment. It draws on data from a postgraduate course for professional educators, delivered globally online, and highlights the relationship between students' online discussion and their written assessed work, arguing that we need to focus on both of these in terms of the writing demands they make on students. In so doing it utilizes a theoretical framework which conceptualizes writing as contextualized social practice. The paper illustrates the complexity of the rhetorical demands being made on students in these new environments of teaching and learning and, in focusing on writing, complements present approaches to online learning which have, to date, tended towards collaborative and constructivist perspectives. The article highlights the relationship between pedagogy, technology and assessment. It concludes with a discussion of the design of an online writing resource to support student writers on this particular masters programme.