The town of Whyville, founded in 1999, has a population of almost 2 million tweens. You won't find Whyville on a map. It's a virtual community for 11- to 13-year-olds that mixes entertainment and education to get kids engaged in learning. To do this, the site lets organizations -- for a small fee -- set up shop and teach kids about topics that include rocket science (NASA), art history (the J. Paul Getty Trust), marine biology (the Woods Hole Oceanographic Institution) and nutrition (the University of Texas and School Nutrition Association). For example, to impart the importance of eating healthy, the community tracks the calories and nutrients citizens eat in Whyville and reports the health consequences of their diets. To show kids how much fun science is, users can play "Solstice Safari" to get a feel for how and why seasons change and "Geodig" to learn about rocks and their characteristics. Since its inception, Whyville "citizens" have designed the site's justice system, set up charities and written for its newspaper. The National Science Foundation, encouraged by its success particularly in reaching adolescent girls, is studying Whyville to see how it can be improved and possibly replicated, and the creators of Whyville continue to work with teachers to make it more useful in the classroom. To learn move, visit www.whyville.net.