Well, this sort of setup would work alright if Sumiko was a typical high school homeroom teacher. Although it would be a bit amusing for her to send them out into the hall, my take on the teacher would be a bit more creative with her punishments, while at the same time hinting that she is also the occult club's supervisor... Specifically, she would probably do something more along the lines of pulling them both aside and subjecting them to her own take on scetch art horror (unshown to the rest of the class, of course) which leaves them somewhat unnerved, to which she then adds, "Please refrain from displaying art during class outside of art class."
If she needed to have them stand in the hall, she would probably use heavy encyclopedias rather than buckets of water as well. Something tells me she would probably have more of those at hand anyway. Other than that, I think its a pretty decent opening scene.