How to controll students in the class makes me puzzled.   

Since I graduated from university, I have been teaching English in senior high school. What's more, my school is the key high school in our province. I always believe that the students will be obedient. However, with time going on, I have come to realize that what I thought before is seriouly wrong. Years ago,the students were obedient and not naughty. They all abided by the school or the class rules and finished the assignment on time and actively studied in the school. But nowadays, all this has greatly changed. Apprently they obey the discipline. Actually they don
't. In addition, for example, today you give them assignment, tomorrow when you check it , you will find that most of them don't finish it. This makes confused very much. And I was very angry with them. Usually I have been strict with them. I have exemplified so much and told them how important studying well is. I often think of this situation over and over again. As a result, I drew no conclusions. Why? I very often say to myself. I always feel this is a headache for me. How to cope with this problem is the key for me at present because I do want to teach them well. What do you think of this situation? Could you let me know??? Tks!!

Have a nice day!!