Writing is a skill which is actively taught in both first (L1) and foreign language (FL) classrooms, yet surprisingly few cross-curricular links are made. This paper, aimed at both practitioners and researchers, presents a framework for designing and implementing a strategy-based, cross-curricular approach to writing pedagogy in schools. It firstly considers the factors which should be taken into account when designing such an intervention in both L1 and FL classrooms. It then outlines the key steps in the implementation of such a programme of strategy-based instruction. To exemplify this, the paper reports on data throughout from an empirical study involving a classroom intervention of explicit strategy-based instruction which was delivered firstly in the German FL classroom, and later also in the English classroom of a Year 9 (age 13-14) class in a secondary school in England. The aim was to help students to develop their writing strategies and to encourage transfer between languages. Findings suggest that while a programme of strategy-based instruction can improve strategy use and attainment in writing within a particular language context, effects are most powerful when there is collaboration between L1 and FL teachers. Evidence therefore calls for a multilingual approach to writing pedagogy.