Scratch

The Games for Learning Institute http://g4li.org/
have announced a contest
http://g4li.org/?news=games-for-learning-institute-and-motorola-foundation-announce-2010-games-for-learning-design-competition
for games that teach 5 of the New York State geometry standards for
6th grade.

Register by: December 12, 2010
Game Submission Deadline: January 12, 2011

There is a flier at
http://www.tiltfactor.org/wp-content/uploads2/Game-Comp-Mailer.png
if you want something to post on the wall.

The game has to run in a browser on a commodity PC or Mac (no special
hardware or special plug-ins), but I think that Scratch games would qualify via the Scratch Player (which only requires Java, and that is specifically ok).