I have a particularly noisy group of 3rd year students this year (14-15 year-olds) for English. 28 people in one classroom. A few tricks I've tried (with varying success): Unannounced tests at the end of the period, kicking people out of the classroom (not literally
),... The system I've settled for is: I give marks for behaviour and co-operation every lesson. People who don't behave, get zero. Their names are called off at the end of the period. If they manage to get three zeros in one semester, they end their asses up in detention (detention in Belgium is on Wednesday afternoon, when all the others are free, and takes 3 hours). That's been quite effective, and the class has calmed down quite a bit. Another thing this group was notorious for, was the shooting of small balls of paper at each other. We took care of that quickly: Anyone caught shooting one, gets to stay after school every day for a week to clean all the classrooms.