The purpose of this study is to clarify the differences of the group effect between cooperation and competition from the point, of educational sociopsychology. For this purpose three variables (group participation, group cohesiveness and group productivity) were introduced, and hypotheses on the differences of these groups on three variables were examined. 523 four-member groups (266 cooperation groups, 257 competition groups), consisting of 6th grade children, were used. The subjects were required to accomplish two tasks (puzzle and discussion problem) in cooperative (CO group) or competitive (CM group) situation. The measure of group productivity is the achievement level of the tasks of the group. In both situations the verbal interactions among the members were permitted. After the two tasks were accomplished group participation scale (SPA) and group cohesiveness scale (ATG) were administrated. The group participation scale consisted of three subscales (solidarity, power and afffiliation scale). In addition to the group cohesiveness scale, sociometric data were obtained before and after the experiment. All the measures were treated as the measure of group level.