Secondary school students are increasingly exposed to texts containing morphologically complex words. Morphological knowledge may help with understanding those words. Appropriate educational materials to teach morphological awareness (MA) are scarce. A design-based approach was used to develop an MA-intervention for Dutch secondary school students. We (1) analysed the aforementioned problem through semi-structured discussions with teachers and a review of previous MA-intervention research; (2) developed a prototype of an MA-intervention in collaboration with teachers; (3) evaluated materials from Step 2 quantitatively through a pilot study with seventh grade students (N = 60) and qualitatively through a semi-structured discussion with teacher educators (N = 4); and (4) reflected on the proposed design principles. Insights obtained from teachers and the literature were implemented in our MA-intervention. Students' performance was related to a measure of general language proficiency. Finally, teachers, students, and teacher educators pointed out several strengths and weaknesses of the intervention. The present study highlights the importance of the following design principles: focus on the patterns in morphology in order for students to explicate their morphological knowledge, suitability of the intervention for students with varying levels of language proficiency, and availability of training and background information about MA for teachers. Collaborating with teachers provided indispensable insights into students' needs, knowledge of MA, how MA-interventions can be implemented and matched to teachers' pedagogical expertise and experience.