with prebuilt computers, its always going to be a compromise. you cant pick and choose each component, so the likelihood of everything being ideal is slim.
that being said, its pretty much a given that most pcs nowadays, even prebuilt, will run osx. where you might have an issue is the audio and lan controller.
you can replace both of those with addons, a usb audo device and a pcie lan card if necessary.
when it comes to building for a school, id advise against it personally.
if you leave those pcs as windows systems, if theres a fault its the manufacturers fault.
if you install osx onto them, and theres a fault, its your fault. is it worth taking that risk with your reputation (guessing youre the IT bod at the school?) just so teachers can use osx? if they want to use osx, get the school to stump up for a few mac minis, with the view to replacing the whole line up with macs.
just because you have built your own system, doesnt mean you are cut out to manage 15. by asking if there about ideal candidates and premade edited dsdts, it just shows that you arent at that level imo.