The ability to argue is an important academic goal in secondary education. This paper reports on an exploratory study which investigated how asynchronous text-based conferencing provides a new site for school students to rehearse and develop their skills in argumentation. The study used linguistic tools of analysis to investigate two key questions: How is argumentation structured in asynchronous text-based conferencing? How do students use language to negotiate their position on an issue? The originality of our study lies in the use of a functional linguistic method of analysis which provides unique insights into how students use language to argue, insights that can inform teaching and learning both in school history (the context for this paper) and more generally. Our interest in language is based on the premise that it is central to the learning process --a premise supported by work in socio-cultural psychology and systemic functional linguistics. The most significant findings to emerge from the analysis were that (1) counter-argumentation was rare; and (2b) the more tentatively a claim is phrased the more likely it is that students will challenge or counter it. (Contains 1 figure and 2 tables.)