摘要：This research aim is to know the students' understanding in adding number up to 20 using traditional game of dakocan and to acquire learning trajectory of adding number up to 20 using traditional game of dakocan for the first grade of primary school. This research used methodology of design research that consist s of three phases, there are preliminary design, tea ching experiment, and retrospective analysis. Subject of this study is 33 first grade students of Sekolah Dasar Negeri (SDN) 98 Palembang as one of partners' school of Pendidikan Matematika Realistik Indonesia (PMRI). The result of this research shows that the students' understanding in adding number up to 20 can be stimulated by using traditional game of dakocan as a context. All of strategies and model that is used by students and also their result discussion shows how construction and contribution of stu dents can help them to understand concept of adding number up to 20. All the activities that are done by students produce learning trajectory to gain the goal of learning. Each steps of learning trajectory of students has an important role in understanding the concept from informal to the formal level. Learning trajectory using dakocan that is produced consist of playing dakocan, put the model of dakocan to the frame ten dakomatika to understand the relation of part and whole of ten combination in adding nu mber, and solving contextual problem in adding number up to 20.
