Every time I see some good behaviour going on - hands up, working hard, helping each other - I click my green counter. Every time I see some bad behaviour going on - not listening, chewing - I click my red counter. You don't even have to admonish the bad behaviour verbally. Just hold the red counter in the air and click it and the guilty party will stop it.
If there are more greens than reds by the end of the lesson, then the students all get house points. If there are more reds than greens, the students all have to stay behind for 10 minutes. It really promotes collective responsibility for learning and students of any age respond well to it - and more often than not greens win.
It can't be used for every lesson as the kids tire of its novelty but for those trouble-spot lessons such as the last on a Friday after PE it can work wonders
Alice Smith teaches in a North London secondary