A bad manner in Japan

In Japan, we have a lot of manners which are considered rude, but not in Canada. One of them is a manner at school. (but I'm not sure if it's special) It is thought to be impolite to eat or drink during class. If you do, you may be thrown out of the class. In fact, when I was in junior high school, I was scolded by teachers for chewing gum many times even though I didn't understand the reason why I wasn't allowed. Even once in a while I was hit when I was eating lunch during class before lunch time. (I made a wall with my textbook to hide my lunch box, but actually it didn't work. It was too small to cover the whole box) Anyway, if you don't want to fall out with teachers, you'd better concentrate on and write down what they say without eating. I think it's quite tough for people who are always hungry like me.