We've been struggling with the same issue. To say it's frustrating is putting it mildly. We've tried rewards of various types, reasoning, yelling, and the rest of the regular options. But they quickly tire of the reward, or it's not "big" enough to motivate them. Yelling, etc only worked if we continued to ride them daily (and sometimes by the minute).
I've rrecently ead some recommendations from a syndicated child/family psychologist that makes a lot of sense to me. So far, it seems to be working. It takes the stress and emotion out of the picture, and puts the responsibility on them. I'll share it with you, and you can see what you think. His website is www.johnrosemond.com if I remember correctly. Here's basically what he says.
1. As long as they live in your house, they need to follow your rules, including the tidiness of their room and other chores.
2. Chores are done because they are part of the family, and each family member has their own areas of responsibilty, therefore "rewards" and "incentives" distract from that. (this was a tough one for me)
3. Doing chores gives kids a vested interest in the family, and allows them to feel like they contribute to it (even if they don't vocalize it). We value things we have to put work into.
4. When you begin to enforce chores, expect them to complain, it's part of being a kid.
Great, so HOW do you do it? Here's what he says about that:
1. Pick which chores each child will be assigned both daily and weekly, and then write out the steps for doing it correctly. This way they have clear instructions that they can always go back to when they "forget" how to do them.
2. Put the chores on a chart where each child can easily check what chores are due on any given day. This could be one master chart on the fridge (for example) or separate ones for each child.
3. The first day, demonstrate how they are done and watch them once/twice to make sure they "know" how to do them.
4. Thereafter, if they do not do the chores, simply do them yourself, without complaint....oh, but wait....when you call them in, or they return to the house, show them what a great job you did on their chores. Then explain that since you did their job, they will be confined to their room for the remainder of the day (or the next if it's too late) as well as going to bed immediately after dinner. That means if they miss some activity or haven't finished their homework, it's their problem. Lights are out, they're quiet, no exceptions, period.
The hardest thing we're having with it is having time to do their chores. But it's been a huge incentive for them, and we're getting far less complaints from them, too.
Hope it helps, good luck!