International audienceThis study assesses preschool children’s understanding of length and area measurement through the activities of a mathematics program in Japan. Japanese preschool children do not formally learn mathematics; thus, we designed mathematical measurement activities for young, less-experienced preschool teachers to implement for nine five- to six-year-old children. We conducted structured clinical interviews with the children individually, both before and after the measurement activities, and qualitatively analyzed the results by comparing their answers and connecting them to the activity contents. Results indicate that children learn to understand direct comparison through activities; however, it is more difficult to establish understanding of measurement by non-universal units