Larry Lowry of the Lawerence Hall of Science introduced me to the term, "collaborative learning." He prefers it to "cooperative learning" because he feels that kids are more likely to collaborate than cooperate!
My problem with traditional cooperative learning is that too often you have kids that only pay attention during their assigned role in the group.
I have students work in groups of 2 - 4 for most lab activities. I do not assign jobs like materials manager, recorder, etc. I do not allow one paper for the entire group either; every child must turn in his/her own work.
Students learn very quickly to work together & take turns to complete the task.
I rotate seating every 3 weeks, so that students work with everyone in the class over the course of the year.