There are a large number of in-class auction experiments to illustrate demand, supply, and markets. They provide a hands-on demonstration of the way markets work, and also can be a springboard for discussion about what it takes for a market to work like the textbook model—and when it does not.

For other examples designed for use in college classrooms, but appropriate for use by high school students, see Games Economists Play.

If you have good Internet access, consider online experiments designed for college classrooms, available without cost at the University of Virignia's Veconlab.