Simple mechanical tasks improve through competition. Competition increases the amount done, but quality remains the same or may deteriorate. To profit from competition, learners must think they can succeed. The more personal the competition, the more it affects the learning. The best competition is with oneself.
More difficult tasks improve through cooperation.
Students learn a great deal from each other. They learn more rapidly from familiar peers than from those who are strangers. Group work improves quality rather than quantity. The gain in the group is only in relation to the interaction that goes on. If the group is working as individuals, there is little gain.