Tops can be made by inserting a piece of a bamboo skewer through the center of a plastic wheel. But it doesn't have to stop there. What if the skewer is longer or shorter? What if you add more wheels? How does having the wheels higher up on the skewer vs. lower affect the performance? Is it possible to add to the top without disrupting it's balance? There is a surprising amount of room for experimentation!
For added longevity, encourage your students to make a top that can out-spin all the others. Make competitions official by building a simple structure to contain the tops to a small area. The arena can be 3x3 or 4x4 sticks as well.
Bending the tip of the skewer will cause the top to jitter and move unpredictably.
Limit the number of wheels your students can use to 5 and encourage them to redesign rather than make completely new ones.
Wheels can be purchased here.