I have an idea how to break habits of bad pupils in a school, this story is a good example what you can do:

Once I heard a radio report, according to it, a school in (oh, I don't remember where it was) faced with a unique problem. Many girls used red lipstick and put it on in the bathroom. That was actually normal, but after they put on their lipstick they pressed their lips to the mirror leaving lots of lip prints.

Finally the director decided that something had to be done. He called all the girls to the bathroom and met them there with the cleaner.

He explained that all these lip prints were causing a major problem for the cleaner who had to clean the mirrors every day. To demonstrate how difficult it was to clean the mirrors, he asked the cleaner to clean one of the mirrors.

She took out a long-handled squeegee, dipped it into the toilet and then cleaned the mirror - since that time not even a single lip print appeared on the mirror :))))))))))))))