Zane, i'd go with either a ball python or a corn. Ball pythons are extremly docile - only ever heard of one person getting bit. My old science teacher kept a bunch of snakes in her class and scared the living begeebus out of us as to what she would do if we ever messed with the snakes cage without her permission. Some girl did while she was out of the room and the bp bit her. But it was interesting how she was able to turn this into a disciplinary action versus the teacher getting in trouble.
any snake will bite if provoked!
Ball pythons every now and then get annoying as to they don't want to eat. Some can be very picky feeders, some dont.
Corns on the other hand aren't that hard to get eating. They are a LOT more active in the cage than a bp is. There are a lot more color choices, and I think they're just a more interesting snake.
Now both of these snakes are generally calm, but what your friend needs to do is take it home and keep it there for upwards of a month and make sure it's going to be docile enough to handle with kids. And suggest to your friend to let the kids take the snake out as a reward for good behavior. If they get rowdy, back it goes. That will be the first thing that will cause a bite - a bunch of kids around talking loud and moving a lot.
It shouldn't be a problem, I know theres a few people on the forums here that have snakes in the classroom. I know one guy over on the rat snakes forum who has a black rat snake he has in his class. You can get some ideas from other teachers im sure as far as the details go... but from what i'm saying i'd reccomend a corn snake first, a ball python second.
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Chondros and colubrids... my 2 favorite types of snakes!
"Life is hard. Life is harder if you're stupid." - John Wayne