Hmmm, well [strictly non-professional here

, so don't be upset if it's not correct.] schools usually depict either youth or learning/education. The snake is a hindrance or some form of conflict that was going after either you as a child or your own child. Something you are looking back upon and wishing you could change, either a bad idea or a conflict which you wished never happened. You're trying to protect yourself or an ideal you have learned as a child, something which is meeting opposition.
Strictly non-professional on my part. I try to use Freudian methods or psychological translation.