As a teacher I refused to get IPADS in my classroom for a number of reasons, many noted in other people's comments above. Along with one that I wish I could quote, but I have forgotten the study author. I read a study a few years ago talking about how schools are failing kids and why the latest increase in technology in classrooms, especially elementary classrooms is actually hurting our schools more than it is helping. Basically it was saying that when we use an electronic devise for writing, or doing math, or even reading our brains are less actively involved in the process. When we write, for example, our brain has to be actively involved in the process because it has to not only hold the pen it also has to move it in the correct direction over and over again while another part of the brain is remembering what to write. Granted, this takes a very short amount of time, however, it is still there none the less. However, when we are simply typing keys on a computer that section of the brain that controls the hand/arm muscles is not activated and therefore a large part of the connections that the brain makes about information are no longer being made. This same effect was there when students were reading books on an electronic devise rather than holding a book in their hands.
I have seen this in kids a lot - add to this that they see an electronic devise as a toy and not an educational devise you increase the likely hood of more time being spent on playing rather than on doing their school work.