The purposes of the present study were to investigate the patterns of change in macroscopic character of sociometric structure in classroom and to analyse the relationships between the patterns of change and the students' cognition(the teachers' leadership behavior, class atomosphere and school morale). Subjects were 807 junior high school students from 22 classrooms. Major results were as follows.(a)The structure of the male groups changed to a more centralized structure within half a year, but the female groups remained diffused.(b)The groups which changed from a centralized to a diffused structure and the groups which remained diffused highly estimated their teachers' leadership behavior.(c)The female groups found greater satisfaction in their classroom life than the male groups.(d)The groups which kept the centralized or diffused structure followed class rules and felt class unity more often than other groups.