Do high school art students want to go out to study and train, but the school won't let them go?

I have also encountered this situation, and said hello to the class teacher, not to let the school know. Formal leave is definitely not acceptable.

The school will not do anything about your student status, but it is always in the hands of others. If things get tough, it's you who will suffer.

Deal with the class teacher. It's simple. He will cover you.