Schools would do much better to give every student a Kindle.
Although reading books works fine on an iPad, reading books is the only thing that works on a Kindle. And reading books is the behavior most critical to learning and becoming educated.
Maybe if the DX price was lowered to normal Kindle price, it would be more appropriate; but at the moment if you are going to shell out 350$ for a Kindle DX, it is wiser to spend 150$ more to get an iPad.
In my experience, for subjects like math or most basic science courses, the quality is inversely proportional to the number of colors of ink used.
The iPad can be completely locked down so noting but your app or task works. You can also wipe it after each user with minimal fuss. It is the perfect tool for sharing though I agree it should be personal to get everything from it.