I was desperate -- every day I went home feeling like I was escaping a war zone -- and so I set up a classroom economy, a variant of what the behaviorists call "token reinforcement." I printed up bills for $1,$5,$10 etc., as in "real" money, set up bank accounts, wage and price schedules, the works. Everything students might want to do cost something, whether it was visiting the restroom between recesses, computer time or using art materials. In turn, they could earn money in a variety of ways.
...I hated the complexities involved, but I did like the results -- I saw a turnaround almost immediately.
Initially, requirements were quite easily met to earn classroom dollars -- so many minutes on task, so many items completed, homework handed in etc. Every week the prices changes (not unlike the real world), and the most valued reinforcers, like computer time, went up in price while less popular ones (like using the library) went down. A by-product of this system is that students got fairly proficient at operations with decimals and real-word money skills as well as understanding some basic economic principles around supply and demand.
...I could have phased out most of the system -- in fact I did "fade out" many of the specific rewards -- but the students enjoyed being little capitalists so much I couldn't shut it down completely.
Don't ask where I was wandering when I stumbled across this.