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The collective working-memory effect is based on cognitive load theory, suggesting that group learning could be more effective than individual learning if the complexity of the material to be learned was high. Sharing the load of processing complex material among the group participants and their working-memories enables more effective processing and easier comprehension of the material to be learned. This assumption was experimentally confirmed, suggesting that
This effect is the result of a trade-off between transaction cost (communication and coordination with the group) and reduction in cognitive load due to sharing the overall load with other group members.2)
Still, the researchers are cautious generalizing the results from laboratory to classroom settings.
A recent study confirmed the described effect, especially in case of medium task complexity: