In the light of international interest in teachers' literate identities and practices, this paper addresses the under-researched area of teachers' writing identities. It examines the multimodal interactive discursive practices at play in the writing classroom of a teacher in the UK who, in order to support the pupils, consciously positions herself as a writer in this context, seeking to model engagement through demonstrating writing in whole-class sessions and composing alongside pupils in groups. Drawing on previous empirical work which explored the fluid identities performed and enacted by this teacher (Cremin & Baker, 2010), the paper, examining video material, affords detailed analysis of the multimodal interactive discourses indexed in demonstration writing and writing alongside. It maps specific instances of discursive practice onto a model for conceptualising teachers' writing identities: a teacher-writer, writer-teacher identity continuum. It reveals on-going conflict between the teacher's intended discourse positions/identities and the recognition (Gee, 2005) and acceptance of these attempts by the pupils. The paper, in contributing new understandings about the microscopic, fluid and conflictual dimensions of identity positioning in these particular practice contexts, highlights the importance of the embodied discoursal voice of the pedagogue. Additionally, it offers a new analytic tool for understanding how teacher behaviour opens and constrains identity positions and argues that multimodal interaction in teaching writing deserves increased methodological attention.