Using language adequately within technology tasks is part of technological literacy. However, this can be challenging for students, and a teacher may need to help students to master aspects of domain specific language that matter for the task at hand. 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'. The interventions were carried out by one experienced teacher in one course, during three consecutive cycles of trialling and improving the curricular design. The resulting design principles for teaching to write about (engineering) design are concerned with: a relevant, complete and feasible focus on language; scaffolding the writing process; procedures for teacher support. For each of these, specifications are described.