Every three months during the school year, we come to this point where the kids bring home this piece of paper with cryptic marks on it hoping that maybe they'll get some reward for all of their hard work during the school year. And every time this happens, I sigh because I can't reward my kids with money. Let's face it: the economy stinks, and if you're used to rewarding your kids with money for good grades, you might just be breaking the bank nowadays. That's how it is. But this summer I came up with a reward system for…