Relation Between Judging Addition of Weights and Conservation of Volume

In a task of judging addition of weights, a U-shaped growth curve was observed (Piage, 1973; Aoki, 1988). Aoki also showed that the performance of them went down in 6 th grade according to judgment and explanation corresponding to criteria. Concerning this curve, Piaget (1973) claimed that this phenomenon was related to the conservation of volume though without empirically proving it. The purpose of this study was to re-examine the U-shaped curve in this task with another corresponding criteria (only judgment criteria), and to clarify the relation between the phenomenon of these weights' tasks and conservation of volume. From second graders to college students, 267 subjects participoted in this experiment with a given problem paper. The results proved that the U-shaped curve could be found again, though sex differences were not observed; and it was found that the relation between conservation of volume and the weights' tasks was observed. It was also confirmed that the achievement of conservation of volume did not always explain every phenomenon concerning this curve.