I used to have difficulty getting the class quiet. Nothing short of screaming 'shut up!' seemed to make any difference. Then I wrote the word 'awesome' on the board. When I had to speak to the entire class, I erased a letter beginning with the final letter. If the class made it to lunch time with the word intact, they sat where they liked. If not, they had assigned seats. If they lost the entire word by the end of the day, the following day they had silent lunch. If the entire word was intact at the end of the day, they were rewarded with 15 extra minutes of PE the next day. The first two days the class was at 'awe' by lunch time and they had an 'a' left at the end of the day. Each day they improved. This past week they had the word intact at lunch two days out of five. It worked for me when all else failed.