This study analyzed elementary school students’ understanding of floating and sinking, focusing on the generalization of their understanding to extremely large or small objects and the effect of perceptual information. In terms of consistency in the judgement of floating and sinking based on kinds of materials, the results showed that 1-2 graders were more affected by the existence of perceptual information, less likely to cite density or material traits for their explanation, and less likely to generalize their understanding to extremely large or small objects as compared to 5-6 graders. However, even among 5-6 graders, just a few tended to show consistent judgement on floating and sinking based on density or material kinds across all items, including extremely large or small objects. Beginning from the object with prominent perceptual traits, and followed by familiar objects, they are considered to gradually generalize their understanding of floating and sinking based on material kinds. The results clarify the developmental course suggested in previous research, by directly asking for children’s judgements on density-related phenomena, including extreme cases or cases without certain perceptual information.

  The purpose of this study was to examine the relationship between intergroup status and physical aggression, relational aggression, and prosocial behavior among middle school students dealing with a status in their peer group. 707 students in grades 1-3 from two public middle schools participated in this survey. The results indicated that relational aggression was significantly positively related to inter-peer group status, while physical aggression and prosocial behavior were not significantly related. These findings suggest that students who belong to a higher status group are more likely to engage in relational aggression. In the discussion, the aggression of students in the high status group was discussed.