Carl and Oliver,* both 8-year-olds in our after-school program, huddled over piles of Legos. They carefully assembled them to add to a sprawling collection of Lego houses, grocery stores, fish-and-chips stands, fire stations, and coffee shops. They were particularly keen to find and use "cool pieces," the translucent bricks and specialty pieces that complement the standard-issue red, yellow, blue, and green Lego bricks.

"I'm making an airport and landing strip for my guy's house. He has his own airplane," said Oliver.

"That's not fair!" said Carl. "That takes too many cool pieces and leaves not enough for me."

"Well, I can let other people use the landing strip, if they have airplanes," said Oliver. "Then it's fair for me to use more cool pieces, because it's for public use."

Discussions like the one above led to children collaborating on a massive series of Lego structures we named Legotown. Children dug through hefty-sized bins of Legos, sought "cool pieces," and bartered and exchanged until they established a collection of homes, shops, public facilities, and community meeting places. We carefully protected Legotown from errant balls and jump ropes, and watched it grow day by day.