Be consistent. Don't change throughout the course.
Positive Reinforcement. concentrating on the bad behaviour praise them for their behaviour. Check out the PBIS (positive behaviour interventions and support) website.
Start strict. Most teachers agree that it's easier to get more lenient than become more strict.
Talk loudly and clearly. Students need to be able to hear you if they're going to follow your instructions.
Plan your lessons. Know what you're going to do and what you need. Have fillers necessary as well.
Play games. Tell students that if they behave you'll play a game at the end of class.
Be clear. Give instructions that they can understand. Write them down if necessary.
Be nice and respectful. You don't have to be mean.
Provide things to do. Not all students work at the same pace. Students get out of hand because they have nothing to do. Keep a couple of extra exercises or games for them to do when they finish. If they're busy, they're less likely to make trouble.
Don't shout. There's probably no way that you can be heard when many students are talking and you're just adding to the noise. Try clapping your hands or ringing a bell to get their attention.
Change the room layout. Separate students if necessary or give them assigned seats.
Keep your promises. If you say that you'll play a game, play one. If you say that a student will be punished you'll have to follow through on that.
Learn more. If you're looking for online courses, check out Leadership in ELT offered by International House.
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