Observe any elementary school playground during recess: children are running, playing tag, throwing balls, jumping rope, hopping hopscotch, playing jacks, hitting, hiding, clapping hands, and singing. To adult spectators, this buzzing beehive of activity may seem chaotic, but the chaos appears only to them. The rules of the games are obscured by the noise and the action; boundaries, forbidden areas, and "it" figures--structures rigorously adhered to by the children. The shared knowledge of these games and the lore that accompanies them binds this community of children together. Friends teach the games to other friends, who discover them as ...