I just found this idea on Mrs. Lee's Kindergarten site. It is a positive behavior system she uses. I have copied the post from her blog for you to look at.
We are building rainbows for good behavior in Mrs. Lee's room! If a child is caught going the extra mile for good behavior, he/she can earn a piece for their rainbow. At the end of the week, if the rainbow is complete, your child will get to choose a treasure from the treasure box.