Balloon Rockets - I've done this in several science camps I've conducted. Kids have fun with it. But, when the balloon deflates it may fall off the straw because it's surface area changes - another good thing to show and explain to kids.
What is S. is an abbreviation for Science Technology Engineering and Math. It is not a particular method or way of teaching, but more of a movement to integrate these subjects into the curiculum with real-world, problem-based activities.