I cut off their crusts now when I make their lunches, and throw them out the back window for the birds right away so that the less eco-friendly teachers don't have to worry about it.
(Bread doesn't go in the worm farm, and I don't have a compost bin yet.)
I often get the kids to throw uneaten bread into the back yard themselves. It's a great activity for them!
P.S. (Added June 13, 2010.) Birds also love cooked rice. Don't throw uneaten rice into the landfill! Set it out on the footpath or driveway for the birds. They will have a big party, calling out to all their mates.
P.S.S (Added Feb 7, 2011.) They go nuts for cous-cous too.