Using language adequately within specific content areas can be challenging for students. In this study a curricular design was developed through a series of trials, with the aim to arrive at general principles for a pedagogy that helps students to write about an engineering (electronics) design. The curricular design was theoretically anchored in ‘genre pedagogy’ and in the pedagogy of engineering and technology. The interventions were carried out by one experienced teacher in one course, during three consecutive cycles of trialing and improving the curricular design. Qualitative data were analyzed using theory-based codes as well as codes that emerged from the data. The resulting design principles for teaching to write about (engineering) design are categorized as: setting a functional writing task, scaffolding the writing process, and a relevant, complete and feasible focus on language. For each of these, specifications are described.