Yes, you can let him roam around, if you don't mind cleaning up after him, because I personally have never heard of a housebroken chicken. They do make diapers for them. How old is he, and what kind of temperament does he have? These are things to consider before letting the chilldren pet him. Ideally, he should have a pen where he can move around, and get used to the classroom situation, before he ever goes out running around. or has to deal with petting. And a big pen is best, he needs room to move around, scratch, stretch, flap his wings, even fly or perch. Chickens are social creatures and two are better, but if you can't do two right now, do consider getting him a friend at some point down the road. He also needs a place to dust bathe, using top soil mixed with a little sand in a box like a litter box works ok. When I say let him get used to the classroom situation, I mean several weeks. Kids (even older students) can be intimidating and it will be a daunting situation for a chicken, honestly, but that's not to say it can't be a fun and rewarding experience for everyone. Once or twice a day for feeding is ok, probably in a classroom situation once is fine. There are several commercial chicken feeds on the market, and we use Purina Flock Raiser mixed with corn or a little scratch grain, but there are other types of commercial feed. He should have some chicken feed, not just corn. There are all kinds of treats available for chickens, commercial and table scraps, but you can read up on a lot of this stuff in other forums on this site. He also needs grit, for proper digestion.
Actually, if I were you, I'd make a coop and run for him at home, and just bring him to the classroom a couple of days a week, and then take him home with me again. Or, if you don't have the facilities to do that, maybe one of your students, or someone else you know, does. That way, he'd have a chance to be outside, and in a more natural environment. And he'd get used to being handled faster too. They ride fine in a pet carrier.