Models' use and adaptation aiming at conceptual understanding of decimal numbers

International audienceIn this paper, we report part of a study carried out within a design research methodology. An initial conjecture was made that included the importance of the hundred square model to facilitate the discussion about decimal number system features and connections among and within different rational numbers' representations. We present how this model was used and why it led to changes into different models, 10x100 grid, and decimat, during the teaching experiment. Finally, we reflect on how these changes inform the initial conjecture