You can't take a dozen people at random, give them a pot of coffee and a box of doughnuts, and expect them to learn something. Groups that learn, communities of practice, have special characteristics. They collaborate directly, use one another as sounding boards, teach each other. You can't create communities like this by fiat, and they are easy to destroy. They are among the most important structures of any organization where thinking matters, but they almost inevitably undermine its formal structures and strictures.
Communities of practice are the shop floor of human capital, the place where the stuff gets made.
Perhaps most intriguing, communities of practice are responsible only to themselves. No one owns them. There's no boss. They're like professional societies. People join and stay because they have something to learn and to contribute.