Several factors have been identified that influence a teachers' use of curriculum materials. This paper focuses on the development of materials as a key factor in this process. Clarification is given on how a sophisticated design of curriculum materials can improve curricular implementation processes and outcomes. An overview of the implementation problems of a curriculum development project for primary science by the Dutch National Institute for Curriculum Development is presented and major problems, symptoms, and study strategies are discussed. The teacher's role as learner, specifically in the initiation phase, is then analyzed. Expectations for teachers are also outlined. A summary follows of a field experiment that was designed to compare and test the effects of use of originally developed curriculum materials with materials that incorporated teachers' needs and suggestions. Differences were found in the nature of the teachers' planning activities and in the students' time on task. The experimental group showed a greater orientation to subject matter content and the didactic process then to logistical aspects and tasks. It was suggested that curricular materials should stimulate teachers to analyze the what, when, how, and why of their own teaching role. (ML)