Grammar matters: How teachers' grammatical knowledge impacts on the teaching of writing

•Teachers' grammatical knowledge influences what students learn about writing.•Limitations in teachers' grammatical content knowledge can generate student misconceptions.•Teachers' ‘applied’ knowledge is more significant than declarative knowledge.

Teaching grammar has been mandated in statutory curriculum documents in England since 1988. Yet despite this, research evidence continues to suggest that metalinguistic knowledge is an area of challenge for many teachers. Drawing on data from a larger study, this paper considers the role of teachers' grammatical knowledge, both content and pedagogical content knowledge, in mediating learning about writing in the classroom. It also illustrates how students' learning about writing is influenced by teachers’ metalinguistic knowledge. The study highlights that grammatical pedagogical content knowledge is more significant than grammatical content knowledge in supporting meaningful teaching and learning about writing.