"You more likely mean because Apple doesn't allow one to publish randomly to their app store? If so, then you're twisting the notions of censorship."
It is not just that Apple has standards for their own app store. Fedora has standards for its repositories, but I would not accuse them of any kind of censorship.
The problem is that Apple has created a computer whose software can only be installed from the App Store, unless you pay Apple a special fee and agree to all manner of unfriendly licenses (on top of those you already agreed to to use your computer in the first place). We are past the point of talking about theoretical risks associated with such a system; Apple already refused to allow political cartoons to run on iPads. If you do not call that censorship, what do you call it?
"Apple's restriction on their app store has nothing meaningful to do with students expressing themselves."
Unless those students happen to be expressing themselves by writing software.
"The whole tablet market would still not likely have been proven without the iPad"
I have my doubts. Apple only marketed their tablet well; they did not invent the technology that made it possible.
"who wants the students hacking on their tablets anyway?"
I do, because like many people, I learned to program by hacking every computer available to me in my spare time. I would not be where I am today if I had not had the opportunity to do so. By surrounding students with computers they cannot hack at will, this school is telling their students that they are not allowed to learn to program in such an unsanctioned way; the students must wait until some teacher comes along to teach them some standardized programming curriculum, and too bad if they had been trying to learn something else. Right now, the students are lucky in that they most likely have a computer to hack at their home; that may not be the case in the future, especially if these sorts of restricted computers continue to gain popularity.
"The last thing you want is for it to be easy for a prankster to create applications that would facilitate cheating or mayhem"
Mayhem? If the school's IT staff cannot deal with the "mayhem" caused by a single computer, they are incompetent.
As for cheating, sure, that's a risk of giving students programmable computers. The answer is not to try to restrict student activities on those computers, any more than the answer to cheating by leaving notes in a bathroom stall is to watch students go to the bathroom. It is not hard to build a computer that can be rapidly reimaged before an exam. It is not hard to deny student's internet access during an exam. It is not hard for a teacher to check for ad-hoc networks during an exam.
Why deny students the ability to learn outside the standard curriculum? Why insist that they must come from families that can afford to buy more computers for them, when you could have the school give them computers to program? We had programmable desktops when I was in high school, and the benefits were clear: there was a club for hackers who just liked to hack (and even a system where they would help maintain the school's network). Back then, we had desktops; it would have been great to have something we could carry around with us.
"You also don't want a system that is all hacked up with 3rd party app store items riddled with trojans that keeps the students from opening their legitimate apps and learning."
Funny how we didn't have this problem at my high school. The reason is pretty simple: misbehaving computers could be reimaged quickly. Students who repeatedly and deliberately installed malware were suspended, no different from students who drew graffiti or broken into other students' lockers.
Your argument amounts to this: students cannot learn unless they are following the prescribed curriculum, so any student who tries to hack the computer that was issued for the prescribed curriculum must be either a cheater, a vandal, or that they will just harm their education by doing things they were not told to do. That is a narrow view of learning and it is the reason so many intelligent kids hate going to school.