The biggest issue with school buildings and caged animals is keeping steady heat. Many places won't allow supplemental heating for fear of fire, and some buildings drop or raise the temperature on nights and weekends to save money. This is flat out deadly for exotic pets. IF they've thought of this and are willing to set up a proper tank then it's not a horrible idea. Tanks can be locked to keep non-authorized personnel out.
If you're really worried, bring up the fact that hermit crabs need the same level of specialized care as most reptiles. They might be thinking it's an easy and cheap pet, but with some education (

) they'll soon know the truth. So long as someone is willing to put the time, effort and money into it, it really could work.
Honestly, cold water fish would be a much easier thing. Like CrabbyEmerson said, it's not without it's challenges, but it's so much simpler than taking care of hermits once it's up and running aside from the time needed.
And again, if they're willing to put the time in and do it right, a reptile would make an awesome addition as well. My local reptile rescue will donate an animal and an enclosure, teach people how to care for it, give presentations on it, and take it back during breaks. It's outreach for them and they love doing it!