We used 7 digit code that was assigned to us. It stayed with you K-12. You could 'prepay' for your meals with a single check. I did that until one day the entire school found out my number was 1008000. Suddenly, I had no money to buy lunch and a large amount of library fines. They couldn't change my number so my parents were forced to give me 2 dollars every day and I knew the librarians very well.
