My wife, who is a professor of education, has been saying this for years. So have a lot of others, as well.
Play = Learning - Benefits of Play
A part of my wifes work is helping teachers learn how to use technology to develop problem-centered, play based learning scenarios. These often will involve some sort of mystery or problem where the students must work together and research for themselves the relevant material to solve the problem or mystery. The teacher then, becomes more like a coach...the kids are learning, and having fun!