Tim's right about the issues. Contracts like those generally intended for the educational or government entity only. Whether or not the vendor wants to let individuals have the same discount is totally up to them. And, in such a case, the school or agency would most likely not be willing to be in the middle.
Another issue is sales tax. A school or a non-profit PTO probably doesn't have to pay sales tax on those purchases. But an individual does. If you avoid the tax by running it through a government/non-profit organization, then you could be getting into breaking laws. As the final "seller" the PTO would be responsible for collecting the sales tax and remitting it the state.
That being said, if you see this as a service that's part of your mission, the vendor is okay that individuals are the purchasers, and if you've taken care of the sales tax, then it would be okay. That would be no different than the role the PTO selling school supply kits.
It's handy to know that if you are a PTO leader you can get the Apple discount. You need to bring in your letterhead or some document showing that you are legitimate, or if you buy on-line you just have to certify that you really do school business. Since my computer is a mac and I spend most of my waking hours doing PTO business I qualify for the discount and have taken advantage of it. I don't know if this works for PC companies like Dell or Gateway or HP but it wouldn't hurt to check.
First, I'm completely guessing as to what's going on, so I have no idea if anything is actually shady.
But I'll give the example I'm thinking of:
Take Apple, for example. I believe Apple has a completely separate discount pricing plan reserved exclusively for educators and schools/districts. Those prices are lower than what consumers pay buying on their own.
Apple has every right to do that and it benefits both Apple and schools.
If the district is trying to help local parents take advantage of the Apple educator's discount by making it look like all the purchases are by your school-affiliated PTO, then I think that would be shady to say the least. If Apple didn't mind, then there'd be no reason to try to run the dollars through funny channels, etc.
Unshady things don't typically need financial shenanigans to be kosher. Just my spidey-sense is all.