This study examined the influence of the kindergarten system on children's peer relationships in a mixed class composed of moved up (kindergartners who were already enrolled in kindergarten the previous year) and newcomer kindergartners, in the first month and six months after start of the kindergarten year. Observing 14 moved up kindergartners and 14 newcomer kindergartners revealed that both groups rarely related to a peer in the first week. Moved up kindergartners related to other moved up kindergartners rather than newcomer kindergartners until the second week. In all observation results, newcomer kindergartners consistently related to other newcomer kindergartners. However, they also tended to relate to moved up kindergartners from the third week. The results reveal that newcomer kindergartners expand peer relationships on the base of newcomer-newcomerrelationships.