We started a marble reward system and it seems to be helping tremendously. My son is eager to do extra chores and so forth... the power of the marble!
We wrote up a list in 3 sections: Expected behaviors, Extra behaviors and Negative behaviors. We based our lists on the ones at
http://www.easychild.com/free-chore-lists.htm which are separated by age. The top section should have things your kids will get marbles for all the time... if they are always going in the negative, the program won't work. We use a mason jar and when they fill their jar they will get a reward of a toy or video game or special dinner out, whatever they choose. If my son starts to have a fit or hit (which is his main issue), we can mention that he will lose marbles. We calmly say what he should do, ie calm down and take a break from X and come back when you are calm, if you hit or fight you will lose X marbles (and may lose privileges as well, like video games or tv). Many times this works as a detterant for the bad behavior. He also never flushed the toilet (ick), he is almost 100% flushing now, since he lost gems for not flushing.
My step son arrives on the 24th for the summer and he has a lot of issues and bad behaviors. We are really hoping the marble plan will work for him, as it has for my son. I'll let ya know in a few weeks!
And since we're going to WDW in less then 3 weeks, I am making a special behavior chart/list for vacation week and will use points instead of marbles, (not lugging down jars of marbles!) and if they get X points at the end of the trip they can get an extra souvenir, price range will be determined by points earned.
My stepson has a horrible behavior of bawling/crying hysterically in restaurants, which is really irritating and embarassing. He is 10.5 and he still did it the last time we saw him at Christmas. So... that will be a huge neg marble/point reducer for him. We ensured that every restaurant we plan to dine at while at WDW has at least one food item he likes on it, so there is no excuse for him to cry. Going someplace like Marrakesh and expecting him to do well would have been a little mean! LOL
I know your guys are a bit older, but I bet this will help. Several of our friends are using this system with good results as well, but we all have little ones.