Since I am usually part of that chatter myself, I do not find it difficult to stop it - I simply stop talking myself. The rest follows.
Many colleagues find it difficult to control a class. I usually put forward that there is not always need to. Not in the eldest of fashions at least. I sometimes take a seat in the middle of the class and rather than control the minds of my students, I let them loose. However, I guide them - without 'guiding' - to get to a conclusion I find important.
Maybe it is my classes being rarely over the size of 10 that allows me to do as mentioned. But still, do you remember when you were 14 years of age? What would have made you listen the moment the teacher enters? Have the courage to temporarily go astray and find innovative ways of teaching.
E.g. I bet if you exchange your seat with the loudest of your pupils, make him try to explain, say, active-passive structures, without embarrassing him of course - that would make everybody listen.
Yours sincerely, Marc