I am also in china, most of my classes are between 50 and 70. Upon reaching the school I found out that my grade 7 students had no english. All of my lessons and language games ended up being filed for later. If I am right in assuming that your students have chinese english teachers, which give english lessons through out the week?

I found that I could keep most of their attention by staying just over their heads. By not breaking them into groups where the discuss things, and picking on the students you know are not listening. I have been able to keep most of the class with me.

For the discipline, and general noise level. I work the concept of being polite into most of my lessons. And slowly they are getting the idea. Having the grade 7's I also reward them with a game at the end of class, if I am able to get through the lesson in time.

For speaking, I have the whole class repeat until it sounds good to me. Then I either have every student say it individually or I count off 1-4, and use the 4 groups to speak at any one time. Thus spreading the group throughout the class.

hope this was of some help