This research examined children's perceptions of junior high school (JHS) and their adaptation to JHS. In the first study, the structure of children's (N=420) expectations and worries about JHS was demonstrated to be five-dimensional by a factor-analytic procedure: (1) worries about interpersonal relationships,(2) expectations about interpersonal relationships and school work,(3) expectations and worries about club activities,(4) worries about school work, and (5) desires for freedom. The levels of expectations were higher than those expected from a previous research. The results also showed that club activities play an important role in children's perceptions of JHS. In the second study, part of the subjects (N=115) in the first study was tested again at the ninth month after transferring to JHS. Cluster analysis applied to them identified four subgroups showing different patterns of expectations and worries, as well as adaptation to JHS environment. One of the four subgroups, which showed high level of expectations in general and low level of worries about interpersonal relationships, was suggested to be most adaptable to JHS.