We just went through this also. We purchased hundreds of Ipad 2's and Apple pretty much said "buy new or forget you".
They are about as supportive of education as a donor do a congressman, only influenced with money.
There are ways to work around Apple update to work with older apps, and there are converters out there which will make most apps for newer versions compatible with older iPads.
I didn't have control over the schools purchasing decisions, or I would have went with Samsung. At least when they stop supporting things, they still allow the older versions to work. But slowly they are going the way of Apple.
Best bet, get a good IT professional at your school, and do network based cloud apps. That way, no matter what device you use, you can always have the best apps for it since it mainly uses connectivity rather than each devices compatibility. This takes a little bit of IT know-how but it future proofs your devices and makes them last a lot longer.