For college it's very helpful. I still use pen and paper for my notes, but I have my textbooks loaded onto my iPad, which is a huge weight saver. Also it helps for when you have to quickly email a professor about something, search the school site for information, or even check blackboard to start on your homework assignments, it's easier to do on the iPad rather than to look for a pc somewhere, or pull out the beast of a laptop to do this simple task. Plus the ipad can sit alongside your notebook or on your lap, where a laptop would just be the only thing on your desk, which would drive me crazy unless it's a computer science class.. Its a very handy tool, recording the class lecture is also a possibility, and if you need a quick spell check or definition of something, google will be right on your desk. The tools this device provides are numerous!
Due note though, that over the past year, I've gotten more and more games which have indeed distracted me during class. So if you are going into a boring class, I'd recommend leaving the iPad in the car, for your educational benefit.
As for high school and grade school, well a student doesn't have a choice in the matter, any electronics found were confiscated (where I come from anyway). If the teachers chose to use iPads in the class, or if the students have permission to use them, then they would be very helpful. But young people are easily distracted and fascinated by these devices, so they could wander from what they are supposed to be doing to YouTube or Facebook. So in my opinion, the iPads would have to be programmed to restrict certain apps, functions, sites, etc.