In Using Cooperative Learning - And What To Do About Them Cooperative educational methods are frequently advocated due, in large part, to the extensive research base supporting their effectiveness. However, they are just as frequently implemented without adequate planning. It takes a lot of skill for students to manage a group of 4 or more.
Smaller groups are more effective and take less time.
Not preparing students to work in cooperative groups. Explain to students why you are using cooperative learning, do a short cooperative learning activity, then have them explain how it can help them. Initially, do short get-acquainted and review activities. Not teaching students appropriate interaction skills. Ask students to contribute to a class list of appropriate group behaviors.