I have been reading a lot about all sorts of great activities that people use for math or literacy centers, and I'm curious to know more about how this works. I live in Spain (I'm American though) and here, although officially we must use a Constructivist approach and adapt for individual differences, in practice it's mostly in-lockstep instruction plowing through the textbook,everyone using the same book, with extra help given as needed. So I'm wondering: what grade levels use centers? How is center time organized? What exactly do you use it for? (I'm guessing practice and review rather than introducing new material.) How much time per day is spent in centers? I'd love to try to introduce some of these ideas over here... Thanks!