I think that's bang on the money, if you'll excuse the pun.
I agree with the "education is free, so should printing be" argument, but the key thing is to consider whether all printing is essential to the kids' education - if you look at much of what they are printing, I'm sure you'll agree that it isn't!
Give them an appropriate allowance in order to print everything they need to do for their lessons, along with some teaching in efficient printing, and charge them for anything in excess of that. While the school should meet the costs of printing homework/coursework, it does not have to fund full-page colour pictures of whoever the latest emo band is.

