I can remember two classes with pets when I was in school, 4th grade there was hamsters and after one school break we came to class to find they had produced babies, and eaten them, baby parts all over. In 7th grade science there was a snake which escaped twice and was never found and there was a rat and a gecko. One day a student had the bright idea of introducing those two, it didn't end well for the gecko. My sister is a school principal currently and she's taken home a guinea pig over summer which is a class pet and I've tried to help out a little with a fish tank in another class, both extremely poorly cared for. I'm not a fan of class pets since it seemed like they pretty much end up neglected, injured or stressed. I would think a ball python would be a poor choice for a class snake since they like it dark and quiet. A boa or hognose or something that is fairly active might be ok.