I think ultimately it really depends what your end goal is. If you are using the classroom to keep the snakes because you cant keep them at home, and if you think of the snakes as your own pets and want to give them the best possible quality of life, then I would go for the rack setup definitely. The reptiles basics PVC rack that someone posted earlier is a great option. The reason I say rack is better is because its much easier to keep the temps and humidity consistent, and it will allow for you to check on them less times in a day, especially because they are at school (not at home where you could check on them more frequently) and because they are in a room in which you cannot control the temps. The rack system will still allow you to use the snakes in your lessons and is probably more economical in the long run. Also, tubs are 100x easier to clean than anything else.
If your end goal is to have the snakes available mainly for the students' learning purposes, then having an enclosure with a nice display would be great. I find the big PVC cages to be a little too expensive for my taste and too big as well. But if money and space isnt an issue, then those are probably your best bet.
Edit: heres my setup by the way. Hatchling rack on the left, and 20 gal glass tank on the right. Eventually they will all be in tubs/racks as soon as I save up enough.
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