Then lay down the law.
But it's lawless in there, sheriff.
You need a bill of rights and a set of rules. Start with the three basics rights, to:
* Be safe
* Be treated with respect.
You, me, the pupils. Everyone.
They build on the rights. Start with:
"Everyone is responsible for their own behaviour."
"Breaking a rule has consequences."
"Do as you would be done by."
Everyone needs to know the rules, to understand their purpose and also to agree to them.
Is that it?
Nope. You will need a few more rules, and the whole school must be consistent in upholding them.
Be positive, fair, honest and straight-forward in policing the rules. Don't get emotional. Have rewards as well as punishments. Give people warnings so they have no excuses - but don't make empty threats. You have to deliver.
Make it meaningful - not "a fierce letting off".
Find out the source of the behaviour and, where possible, diffuse a situation before it becomes a problem, by distracting or using humour.
And when it comes to punishments?
Persistent breaking of rules and abuse of rights deserves punishment. Use a sliding scale of withdrawal of privileges, extra work, letters home, isolation and exclusion - but always leave a path open.
Remember, pupils who choose to abuse the rights of others have chosen their own fate.
OK sheriff, I'll show 'em.
Don't forget your six-shooter, marshal. I'm right behind you..
Duncan Grey is a former teacher and writes on education. His book First Aid Teaching is due out this spring