I have to weigh in on this one...I was basically raised in a petshop (Grandfather owned one) and worked in Vet's offices growing up, blah blah blah!
LOL!
If y'all are wanting an animal to get out and play with, a rat is the way to go. I agree, the males are more of the "lap dog" style, that are really laid back and just want to hang out on your shoulder or in your lap. The females are higher energy, and smaller, but love to be entertained. They are great for games (mine played fetch) and mazes, etc. They are really clean and are practically odorless. Not to be crude, but the males are "obviously males" so you might want to take that into consideration. Some people don't like their "parts" hanging down when they are holding them. Just wanted you to be aware.
Snakes are always cool, BUT, there are a lot of people that wouldn't like them being fed mice, etc. Even frozen ones, so that might not work out.
Rabbits, mice, hamsters, gerbils, guinea pigs, etc, can all be smelly and messy, and can bite. It's hard to get one that enjoys being held. Guinea pigs can also be extremely loud, and that might be distracting in a classroom.
Ferrets are cool, but expensive and need a lot of socialization when they are little.
Tarantulas are really cool, but feeding them can be difficult. I'm not sure where you are, but crickets and mealworms (for lizards, etc) can be hard to find, or hard to find a good source.
I had a hedgehog once. Emphasis on the HAD. That thing hated us! LOL! Would go out of its way to get out and attack our toes to the point of bleeding! Never bit our hands, but I was terrified of it! LOL! Didn't want it around the kids, either. Plus, while they are "cool" they aren't over cuddly.
I would definitely go for the RAT. Just decide what you want to do with the rat.
Do you want to do races? Mazes? Obstacle courses? Get a female.
Do you want to have someone that will wander around visiting, hanging out, and curling up on your shoulder? Get a male.
They are both super friendly and smart. Females just seem to be a little more motivated. LOL!
Good Luck!
Shelly