ABSTRACT
This chapter describes a lesson where the Double Number Line (DNL) was used in order to develop multiplicative and proportional reasoning. The DNL has been used to enhance students’ understanding of proportional reasoning; however, its use is not widespread in UK classrooms. The lesson took place in an elementary school in Tokyo, Japan with 28 students. An experienced classroom teacher, who had been teaching for over ten years and had taken part in several lesson study cycles, taught it. Students can have many misconceptions related to multiplicative structures, particularly when multiplying and dividing decimals, where earlier methods often fail. The DNL has obvious links with the single number line and shares that model’s strength in dealing with continuous variables and decimals. The DNL can assist in the development of multiplicative concepts through its close relationship to measurement and its concrete support toward seeing proportional relationships.
