What a wonderful post. I have been struggling to apply some of what I have learned about play and exploration from the Exploratorium to classroom learning. I’m even organizing a session at Ontario AAPT on “What can we learn about learning from research in museums, media, and other informal environments”. You’ve got a really nice model here, of interspersing lessons with some opportunities for open play. I remember hearing about a teacher who had a table at the back of the room with all sorts of random things — gears, toys, odd machine parts, etc. She never referred to the table in the entire course of the class, but things would appear there from time to time. Much like your students with the spring and bike wheel, students would stop by and fiddle with things on the table. One student remembered the things he discovered from that random assortment of things much more than he remembered the science lessons. Interesting idea.