The intention of the present study is to know how the pupils can learnto make a group of ten to understand the idea of unitizing. The pupilswere given a contextual problem “Counting the Beads” in order topromote their understanding about the idea of unitizing. The process of designing the problem was based on the 5 tenets of Indonesian Realistic Mathematics Education (IRME). The methods of this study was a design research. The researcher designed the Hypothetical LearningTrajectory (HLT) befor conducting the lesson in the classroom. Theresult of this study showed that the pupils learned to make a group ofany number then moved to make a group of twenty before using thegroup of ten as a strategy in finding the amount of the beads. The pupils set a stucture of objects with a help of grouping to ten strategy to understand the idea of unitizing.