We used tiny, wearable computers to create "participatory simulations" for a new generation of educational activities in which students could learn about dynamical systems by actually participating in simulations of the systems. For example, students could simulate the spread of an epidemic in which a "virus" jumps from one wearable computer to another. Our preliminary analysis indicated that the combination of physical and computer interaction lead to a richer learning experience than was possible with traditional computer-simulation activities, or with traditional group activities without computer support.