An ipad that comes with GPS built in will have a sim card slot, thats how to make sure you get the right one.
I would highly recommend a ipad mini as the size is extremely convenient and get one of those protective enclosure cases for it, so it can take the rough treatment.
The only negative point I can think of is that its a added distraction and more time eyes down instead of out the window or watching the student, and not something you really want to set as an example for the student to follow.