Design research can be characterized as a research approach in which the design of educational materials is interwoven with the development of theory. Design research aims at educational innovation and it has a cyclic character: development and prediction, teaching experiments and reflection and revision form an iterative process. In design hypotheses, as in other research approaches, hypotheses are formulated preliminary to the data collection. However, in design research these hypotheses are continually tested and revised during the teaching experiment. Design research cycles typically consist of three phases: preparation and design phase, teaching experiment and retrospective analysis. The results of the retrospective analysis normally lead to new designs and a follow-up cycle. The hypothetical learning trajectory is an essential instrument during each phase of a design study, though plays a different role in each phase. Design research is not an easy approach but valuable as it offers a unique opportunity for learning to understand students’ thinking and learning