This inquiry explored the metalinguistic reflections of 12 students, aged 14–15 years, undertaking a unit of work focused on reading and writing non-fiction. The unit embedded contextualised grammar teaching into preparation for English Language examinations. Students were interviewed twice, with prompts to debate a sample of argument text in interview one, and a sample of their own writing in interview two. The interviews and subsequent assay drew on Gombert's taxonomy of metalinguistic understanding, focusing on metasemantic, metasyntactic and metatextual reflections, and probing students’ capacity to link these to metapragmatic concerns. Similarly to former studies, the findings propose that students struggle to articulate the impact of metasyntactic choices; however, here it is proposed that this may be a special artefact of the need for a specialised metalanguage for debating syntax. Results also point out a tendency to reify form-function relationships, and signal the potential benefit of using students’ own writing as a platform for exploring authorial choices. Finally, the inquiry contributes to the theorisation of metalinguistic understanding by proposing how declarative knowledge may appear from procedural activity, with interviews scaffolding students’ skill to articulate what had initially been tacit language choices.