I’ll suggest Gerbils.
I have mice, and they’re my FAVORITE of the small pets, but they’re most active at night. Plus, they’re very sensitive and don’t live longer than a couple of years. And most petstores don’t have well-socialized, well-bred mice. They have inbred, factory-bred mice that explode in terror when they come across your hand in their cage. Not saying they don’t make good pets, as none of my mice are well-bred specimens. When I look for mice, I look for the ones with laid-back, friendly personalities, and there are a fair number of those out there. Males can be stinkier (they give off a sort of fritos aroma), and they have to live alone (and thus will be happier if they can get regular attention), but females don’t smell hardly at all and can live in groups. Since they live in groups, they don’t care too much about people, preferring to stick with their sisters, so you don’t get that bond that you can get with males.
I also have Guinea Pigs, and I absolutely CANNOT suggest them as a classroom pet. They need a massive cage, and need to live in groups of at least two. They poop a LOT, are LOUD (seriously, every time someone rustles a piece of paper, the pigs will be screaming and raising a ruckus), cost a LOT of money (for a proper diet, you’ll be looking at around $20 a week in veggies, which adds up to at least $900 a year. No kidding.), and they live a long time, up to 10 years. They’re great pets, but they aren’t beginner pets. They require a lot of work, money, and time.
Now, Gerbils are a good choice. They’re active pretty much at all hours, and just like mice, they look really cute when they sit on their haunches and munch away at some morsel of food. They’re cool to watch when they’re digging their tunnels. They’re desert animals, so they don’t drink much and that’s why their cages don’t need as frequent cleanings as mice and guinea pigs. They can be skittish, but they’re also bold little guys who have no sense of self preservation (mice are afraid of heights, whereas Gerbils will walk right off your hand and tumble to the floor). My mice have to be encouraged to step onto my hand, and they’ll keep hesitating and stepping off, stepping on, stepping off, then finally climbing on with all feet in my palm. My Gerbils, they’ll come right up to my hand, sniff, jump on, sniff, jump off, then around and climb on again, jump off and find something else to do. If they’re sleeping somewhere in their tunnels (I have them in a 20gal tank that’s filled halfway with aspen shavings, and they use their desert animal instincts and create a labyrinth of tunnels), I just have to lift the lid and ask if they want “nummies” or mealworms, and they both come peeping their heads out of the bedding. They LOVE their mealworms. They’re agreeable brothers, but if one has a mealworm and the other doesn’t, a chase is on, even if I’m frantically trying to dish out a 2nd mealworm. They’re funny boys.