A great post written by Roger Meike about teaching physics using wireless sensor networks. He used Sun SPOTs and a little bit of science magic to give kids a ball that could tell them how high they could throw it. To achieve this, he embedded a Sun SPOT in a foam football. He set up that Sun SPOT to stream accelerometer data to the base station and then had a host side application that could tell how high the ball was thrown.
The experiment, as well as the code, can be found here.