Change groups often enough so no-one gets stuck for long periods with a difficult class member. Not doing cooperative activities often enough for students to develop cooperative skills. Have students do something cooperative at each class session to reinforce positive cooperative habits. If nothing else, have them share what they learned with a partner. Not planning cooperative lessons with care.
Many teachers confuse group work with cooperative learning.
They put students in groups, tell them to work together, and wonder why the groups aren't successful. Learn how to include them in each cooperative lesson. Assuming that cooperative groups can handle complex tasks before learning how to complete simple ones successfully. Students must be taught how to learn together. Start with short, simple activities and progress to longer and more significant ones as your students are successful.