Why not OS X ?
Because for OSX you should have at least 256MB RAM if not 512MB, plus a decent speed CPU? My 450Mhz G4 with 1GB of RAM is right on the outer limit of acceptable performance.
steep system requirements.
Xubuntu is a free upgrade. a memory upgrade is not. Especially in the context as originally posted.... a classroom.
I don't buy into the media's BS that the school is falling appart under the evil bush regime, but if they can continue to use existing computers with free software, that's good use of our tax dollars. Might prevent a future tax increase, who knows.
Even with as cheap as ram is, not all of us can afford that. I happen to be one of them. Ram isn't in the budget.