The best use for the iPad is the Kindle or Nook app, that allows kids to download and read books on it. It's much easier to develop kids as avid readers when they have such easy access to an endless supply of series books, science fiction, romance, etc--all the kinds of reading school libraries don't tend to carry.
Avid readers read better, write better, follow oral arguments better, bring together disparate ideas better, and have wider frames of reference that make all learning easier.
Is it too expensive to allow kids to download lots of books? Look at all of the money spent on other things--school sports, high tech equipment, standardized testing and curriculum--the list is huge. Just divert a little of that money to give students an Amazon or B&N account.