The rich body of research on dialogic, exploratory talk points to its significance in developing and securing student learning (Alexander, 2018; Gillies, 2016; O'Connor & Michaels, 2007; Reznitskaya et al., 2009). More recently, this body of research has begun to consider dialogic talk specifically in the context of literacy education (for example, Boyd & Markarian, 2015; Edwards-Groves & Davidson, 2017; Juzwik et al., 2013; Wilkinson et al., 2015). However, there remains a dearth of research which considers the role of dialogic talk in the teaching and learning of writing, and particularly its role in supporting developing writers' metalinguistic understanding of how linguistic choices shape meaning in written texts. This article will report on qualitative data drawn from a national study, involving a randomised controlled trial and an accompanying process evaluation. The study involved an intervention which was informed by a Hallidayan theoretical framing of metalinguistic understanding which sees grammar as a meaning-making resource, and which promoted explicit teaching which made purposeful connections between grammatical choices and their meaning-making effects in writing, and which promoted the role of dialogic talk. Specifically, this article will consider how teachers manage this metalinguistic dialogic talk about language choices in the writing classroom.