This article explores the complex relationship between writing in the secondary school classroom as a tool for learning and the dialogical communicative processes involved in crafting and revising talk and inner speech into written speech. A theoretical framework is introduced from the work of Linell, Mercer, Vološinov and Vygotsky to develop a language of analysis for the dialogical processes involved in classroom composition. The framework draws on the concepts of the dialogical self, semiotic mediation and recontextualization. Empirically, the article reports on data from a qualitative case study of a state secondary English class for 13-14 year olds students in the UK that follows a sequence from classroom talk to a written text involving four students. The findings suggest that classroom writing that develops from socially mediated activity can become a dialogical tool for meaning making. The data reported on in this article challenge assumptions that dialogic classrooms are always spaces of concord and agreement. Critical incidents of discord, whereby students challenge, debate, argue, and ultimately recontextualise meaning, can be important precursors for some