Thomas Lindsey, Calvin Farrow and Ethan Grundewald work on their land sled project Wednesday during Club Invention in Blue Earth.

BLUE EARTH — Fifteen soaking wet children eagerly watched their teacher fling a ping-pong ball over their heads using a yard stick and egg-carton section Wednesday. The lesson was about levers, and the students were watching the airborne demonstration in an attempt to identify the fulcrum. (It was the instructor’s elbow.) In the rear of the classroom, the floor was cluttered with plastic bags, bubble wrap, parts of home-improvement projects and other flotsam — items students were asked to collect from home and bring in. These first- through fifth-graders are participating in Club Invention, a half-day program taught by local teachers for four days. “On the first day I asked the students, ‘Who brought in garbage from home?’” said instructor Roger Schoenfelder. “They all raised their hands. I said, ‘None of you did. You all brought in treasures to build with.