I found a comprehensive review of the research in this area by Ann Robinson, Ph.D., University of Arkansas at Little Rock, December, 1991. From Dr. Robinson I learned that the model of cooperative learning is based on virtually no empirical data. To restrict access to appropriately advanced curriculum and to retard the rate at which academically talented students move through the curriculum by organizing instruction in grade level cooperative learning groups for the majority of the school day is not defensible and may result in boredom and repetition for these students. Members believe they are responsible for and benefit from one another's learning. Members promote one another's learning by helping, sharing, and encouraging.
Members are accountable to do their fair share of the work.
Members regularly process how effectively the group is functioning. Learning material with the expectation of teaching it to others results in learning it at a higher cognitive level. When they work with classmates who don't care about the work, or when they repeat already mastered work, they may become frustrated and bored. TAG students don't accept inferior work and so dominate the group or do all the work themselves. Gifted learn humility and democratic values much better by being placed with their intellectual peers.