Cool new initiative from Valve:

STEAM for SCHOOLS is the educational version of Steam, specially designed for use by teachers and students in a classroom setting either in a school or an afterschool or summer program setting (site). All functionality that isn’t core to the education experience has been disabled in this special version of Steam. The only game available through STEAM for SCHOOLS at this time is Portal 2 and the Portal 2 Puzzle Maker.

Check out the lesson plans.  Cool for hip, young physics teachers.