This article draws on data from a national study, involving an experimental intervention with 54 schools across the country, in which teachers were mentored in a pedagogical approach involving explicit attention to grammatical choices and which advocated high-level metalinguistic discussion about textual choices. The research focused upon primary children aged 10-11, and in addition to statistical analysis of outcome measures, 53 lesson observations were undertaken to investigate the nature of the metalinguistic discussion. The data were analysed inductively, following the constant comparison method, with an initial stage of open coding, followed by axial coding which clustered the data into thematic groups. The analysis demonstrates the potential of metalinguistic talk in supporting young writers' understanding of how to shape meaning in texts and the decision-making choices available to them. It signals the importance of teachers' management of metalinguistic conversations, but also the role that teachers' grammatical subject knowledge plays in enabling or constraining metalinguistic talk. The study highlights the importance of dialogic classroom talk if students are to develop knowledge about language, to become metalinguistically aware, and to take ownership of metalinguistic decision-making when writing.