Cooperative Learning in the classroom: "Students learn best when they teach each other" says Sir Ken Robinson

I have been working with learning centers for a few years now and students seem to love it! (just for those who are not familiar with learning centers: they are areas set up around the classroom that present activities designed for specific purposes ex: a math center, a science center, a reading center, etc...). I find that learning centers are great for high-energy classes that have disciplinary challenges.
I presented a workshop in the last AASSA conference on "Cooperative Learning and Assessment in learning centers". Check the attatched powerpoint presentation for a brief overview.
The teachers who were present questioned me about dealing with students who need more support and are not 'great academic students'.
Research shows that when a student models a certain ability or skill to the group, the other students feel more confident and comfortable to have a go next time. A student might observe how another student tackles a math problem, or articulates a sentence and already feels comfortable in knowing one way to deal with the questions and tasks posed.