mentioning the corn field mishap?), we made a little game of it. For every good thing they did (helped each other, knew a small fun fact, etc.), they got a point. For every time they complained, whined, or did something bad (like walk too far ahead), they got a point taken away. If, at the end, they were in the positive, they got a treat. If they were in the negative, they had a consequence. I'm happy to report they loved the game, did really well, and were all plus 5-6 when we were done.
They responded so well to the game that it's kind of been the new thing around here. It works the same way, for every time they do something good (chores without asking, helping each other, etc.), they get a point. And, when they do something bad (whine, hit, say mean things), they get a point taken away. When they get to a certain allotted amount, they get a prize and the prize changes reguarly. Plus, they love that we keep track on a small chalkboard we have. Right now, the prize is 10 points = free chore. Meaning, they don't have to do it, and 20 points = an extra dollar in their allowance. Some days I'm better at keeping up with it than others, but so far this has been the system that's worked best for us.