This study investigated 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 discuss a sample of argument text in interview one, and a sample of their own writing in interview two. The interviews and subsequent analysis drew on Gombert's taxonomy of metalinguistic understanding, focusing on metasemantic, metasyntactic and metatextual reflections, and probing students' ability to link these to metapragmatic concerns. Similarly to previous studies, the findings suggest that students struggle to articulate the impact of metasyntactic choices; however, here it is suggested that this may be a particular artefact of the need for a specialised metalanguage for discussing syntax. Results also indicate 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 study contributes to the theorisation of metalinguistic understanding by suggesting how declarative knowledge may emerge from procedural activity, with interviews scaffolding students' ability to articulate what had initially been tacit language choices.