Tell your students they can work with whomever like in the class, and on whatever project they would like to work on. They must come up with a problem to solve or a project to tackle. You may wish to help them with advice on how to find the necessary information - depending on their level. Then let them go for it! In a twice a week class, give them two class periods to work on it, then they give a presentation on it in class three. They must talk about their discoveries. So they come up with the project then share it with the class.
Level: Jr high- University. (Inspired by an idea in Daniel Pink's book, Drive)