I would follow through with this. Above all, stay calm and composed. While education is important, this issue is less about everyone's opinion of snakes and more about other parents creating a hostile learning environment for your son. It's very tempting to use this for our cause, but other people will better relate to your son's pain, not the snakes' (considering the snake is still safely tucked away at home), and more likely to make changes that way.
For the superintendent, tell them how the teacher confronted you over an unfounded rumor one of the other parents told her. Instead of asking you if you had any concerns, she was defensive and unreceptive to your attempts to clarify. Between the original incident with the other parent and the subsequent conversation with the teacher, you feel that your son is being targeted and punished for circumstances outside of his control, and you feel alienated by not only this other parent - but the school system itself. Does this school make a habit of championing the bias of certain parents? Before, one would assume school is a place for education, not a platform for adults to threaten bodily harm to children's pets. There's an uneven power dynamic there that's wildly inappropriate and some could argue it's emotional abuse.
If the school board plays nice, and if you're comfortable with it, talk to the science teachers and offer to bring an ambassador reptile in, in line with one of their curricular units. THERE is your opportunity to help educate the public.