In my (albeit limited) experience, I've had calm snakes, firey snakes and a couple in between. The one I had bought as a hatchling has yet to even so much as hiss and it's been three years. The fire I have came with a warning: "she bites." She hisses alright, but she's yet to lunge or actually hit me. I'm not suggesting she won't tag me in the future, but she's a lot calmer when I go in confidently, as opposed to erratically moving my hands around in her face. She's settling down more now than she was when she was with her previous owner.

That said, I wouldn't trust my calm ball python not to tag a kid any more than I would trust the fire. Not only can you not trust the snake, you can't trust the kids either. One of them may be flighty, or too rough, or oblivious. A calmer BP will help, but calm only goes so far if someone is scaring them. Some people just can't read animals well or know when to stop. If it were just you, I'd say give the snake some time. If kids are involved (even high school kids, in a classroom setting) I'd say "look only" or find a different pet. Maybe a small tortoise, captive bred blue tongue skink or bearded dragon.