Classroom Management in China can be challenging, especially if you don't have a co-teacher. Here is a strategy on how to involve the Homeroom Teacher (Banzhuren, 班主任) when they aren't in the class.
In my classes I don’t generally have a co-teacher. What do I do if I have a problem student that I can’t handle or something happens in class that’s beyond my control? In my school, there are photos of each class with their head teacher bānzhǔrèn 班主任. I take a picture of this and if I have any problems with certain students then I can go to the head teacher and point out the problem student and explain the issue. If the head teacher doesn’t speak English, I can send the picture to my English speaking contact teacher and circle the problem student and ask the contact teacher to explain the situation to the head teacher.