Well this may not be as major as what you guys have seen, but at my school the students have set up a tutoring program where people volunteer their time help tutor their piers. The group meets in the school library a few days a week and many students participate (on the giving and receiving ends).
This program has helped many students raise their grades up, and from what I've heard the student tutors even enjoy it too.
Oh, and teachers donate their time for this also.