Groups stay together long enough to complete the project. The projects are done outside of class time. Groups have 3 or 4 members depending on the number of students and the activity. Students have a group goal and must work cooperatively. Everyone must be able to explain the strategies used to solve each problem.
Positive interdependence creates peer encouragement and support for learning.
It happens, unfortunately, that one or more group members do not or will not do their share of the group work. It may be because of a domineering attitude of someone else, because of lack of interest, or a host of other reasons. See the explanation.