So much depends on the individual gator's personallity that you can't make a blanket statement that covers it. In general though, I would say that if the gator is comfortable around people, meaning it has been around people frequently without freaking out, then it will probably not be too stressed by the experience. Use one that is a couple years old because the hatchlings and juvies are frequently over-stressed to the point where the just shut down. This usually recognizable by closed eyes and very little movement. Many interpret this as enjoyment or relaxed because those body signals are what we look for in people - but it's not that in crocodilians.
I think the school visit can be a very positive thing, just make sure you take every precaution. My advise is to always bind the mouth if the kids are going to be able to get close to it - even with the head of the animal pointed away and kids touching the tail, inevitably one of them will get a hand close to the gator's head. Any incident could be devastating to you, the school and the hobby.
Bill