© 2016 Elsevier Ltd This paper serves as a theoretical framing paper for the Special Issue, exploring how talk is a mediational tool for learning about writing, and particularly for developing thinking about shaping meaning in writing. It considers Vygotsky's (1986) thinking about language as a tool for learning, specifically here, language as tool for learning about language, hence metatalk. Drawing on Vygotsky's view that writing demands ‘deliberate semantics—deliberate structuring of the web of meaning’, it explores how this notion of deliberateness is developed in the writing classroom, and is manifest in metalinguistic understanding. One particular lens through which to consider metalinguistic understanding is Vygotsky's theory of concept formation. Considering primarily how children develop understanding of the concept underpinning a word, he also addresses how children develop understanding of scientific concepts. In the case described here, grammatical terms are considered as scientific concepts, but so too are other culturally-shaped ways of talking about writing which involve specific understandings, such as drafting, genres, or reader awareness. Vygotsky discriminates between the concepts of everyday life and everyday talk and those specific concepts which form the focus of direct instruction in the educational curriculum. He argues that concept development occurs through two processes: generalization and systematisation. In generalization, the learner identifies and abstracts the attributes of a concept, and in systematisation, the learner is able to organize ideas and concepts based on their properties and relationships. This paper argues that metatalk about writing creates the dialogic space for developing this scientific understanding. This idea is further developed in the light of Bakhtin's thinking about dialogicity, and how written text is always a dialogic interplay between the writer and the reader, not a monologic act. Moreover, in school, learners are writing in culturally-determined contexts which are powerful influences on the writing produced and how it is valued. Classrooms are multi-vocal sites imbued with often tacit norms and expectations about writing, with multiple discourses co-existing in the same learning space, and with learners who present differing beliefs, values and identities as writers. To that extent, the dialogic space encompasses the intersection of the text, the writer and the context, both the immediate situational context of particular classroom communities and the broader cultural context. Creating space for talk about writing can give voice to the silences, the tacit understandings, and the multiple discourses that surround learning to be a writer. Finally, this paper draws together the Vygotskian and Bakhtinian perspectives by considering the particular role of the teacher in enabling and managing these dialogic spaces, generating rich opportunities for talk about writing, and mediating the multiple discourses of both the classroom and the wider curriculum, and assessment, context. Here Bernstein's notion of ‘recontextualisation’ is used as means to explore how teachers mediate their own beliefs as teachers about writing, their pedagogical and subject knowledge of writing, and their professional understanding of learners’ writing needs as they initiate and foster metatalk about writing.