Here's how it works. Each day they are assigned 4 chores of our choice. I've made several different stars/chores to choose from. Each day they complete all four by moving them from the "to do" side to the "done" side after actually doing those chores, they get to move the bottom magnet over one spot. After 7 days (or sooner) they get to choose from the prize box. In the box are toys, stickers packs, and of course CANDY!
They also get chances to move that bottom magnet over for special chores, doing their daily chores without whining, or helping the other finish their chores. I also use it to catch each other up. Sometimes one of them refuses to do chores so they don't get to move a spot closer to the prize. So a few days later I may offer a special chore to catch up.
It seems to be working pretty well. I'm very pleased with the fact that my boys know that they have to help out. It's certainly not perfect and requires consistency on our part. It's been over two months now and we're still sticking with it though so I'd say that's pretty good!