If your school is on a budget, then you might consider the cheapest Chromebooks available. Two of these are the HP G4 and the Lenovo 100s. Both are available from a lot of merchants. Both provide what you will need for students. Fast, sturdy, usable--everything promised in a Chromebook. If you need the other bells and whistles, take a look at other models. If you need basic one to one computing for all students, then both of these models work.
One difference might be the single add-on you need. Both of these models have Cranium screen protectors available. HP here. Lenovo here. The difference might be exact fit. I own the Lenovo 100s, and the Cranium (according to the seller) would not be as perfect a fit as on other Chromebooks. But mine works fine. And my $150 Chromebook looks like a more expensive machine, and I can use the whiteboard during presentations.
The basic idea, whether you opt for the $250 Chromebook or the $150 models, is that you get a lot of computer for the price. If you want it to keep on computing, then add a Cranium for $20.
If you have a bulk order for these or other Chromebooks (they can make Craniums for any model), then use this contact form on Educabana.