I am working on using Second Life in the classroom. I let 3rd graders explore The Learning Experience undersea world exhibit the other day. They controlled my avatar to explore this virtual sub-marina. They were so engaged they didn't want to stop. and I learned how to make my avatar FLY at super high speed!
http://tleinsl.blogspot.com/2009/04/scuba-class-uses-tles-underwater-sea.html

next week we are going to the PADI site - Dive World