Once rules are established, meeting in process... you find chats going on, stop talking and stand saying nothing. The quiet is usually enough to catch their attention. Sometimes it is best NOT to say anything. When you speak again if chatting starts, do the same thing. You will be surprised how fast your class will learn not to speak out of turn. You have actually gave them the floor... They really do njot want it. You gave respect and they are being taught to respect back. :) :) :)