One side effect of taking science lessons into classrooms is that you often get a pile of cards. Above is a fine specimen from taking our home-built bike-pump-powered rocket launcher into a second grade class last month for a lesson on forces and motion and how to control variables in experiments. Lucky kids.
Chad and Nimue built the rocket launcher using instructions from MAKE magazine; I improved on the rockets by making them out of craft foam covered with clear packing tape to make them more durable. Make one, and you too can be loved by elementary school students! (plus it's just entertaining to send the rockets zinging several hundred feet into the sky using nothing but air)