Their task is carefully designed to be suitable for group work. There is positive interdependence - cooperation is necessary for students to succeed.
Students are individually accountable for learning and participation.
The purpose of cooperative learning groups is to make each member a stronger individual in his or her own right. Individual accountability is the key to ensuring that all group members are in fact strengthened by learning cooperatively. With individual responsibility within each group being so vital to the value, learning level and enjoyment of colloborative learning, any one not really participating in group meetings, research, discussions, etc. needs to immediately become involved, or be excommunicated from and by the group. Please, groups, do not be hesitant, for the sake of your own learning experience, to confront any non-participants and to excommunicate any one who has not done what others in the group have needed to do. Don't give any one a free ride.