First language (L1) and foreign language (FL) teachers in schools in England are both teachers of language, yet often have different approaches and priorities when it comes to the teaching of writing and surprisingly few cross-curricular links are made. This chapter reports on data from a study examining how an explicit focus on metacognitive strategy use within a secondary school foreign language (German) classroom in England impacted students' strategy development and writing in the foreign language, and whether any such effects transferred to the first language (English). This is explored primarily through an in-depth case study of one student's negotiation of the intervention of strategy-based instruction over the course of one academic year. Findings indicate that the FL classroom, where students are more aware of being consciously and actively engaged in thinking, is highly conducive to the development of language-related metacognitive strategies, which can also positively affect writing in the L1. Transfer between the two contexts is facilitated further when the links between strategy use in the FL and L1 classrooms are made explicit.