Any iPad would do, if you mean the iPad 1 or 2.
iOS is a very secure operating system, more secure than most computers.
The iPad is a great edicational tool, I use mine every day to do research, take notes, and other school stuff. (10th grade)
As for theft prevention, the iPad is a very robust device. Not easy to vandalize. If you are worried about kids destroying them, then that isn't really something you can prevent. The "bad" kids will attempt to destroy them. But that is just something that you or the teacher would have to monitor and regulate somehow.