My fifth grade teacher had an economy set up in their class with paper tickets as currency. There were various roles most of which I forget. They had a stock market associated with it that was linked to the number of books checked out of a given row/section in the school's library on a weekly basis. Every week the class would go to the library to return and check out up to three books. A lot of kids only got one or two out. I started paying kids to check out books in sections where I held positions with the understanding I would keep safe and then return their book(s) for them - they only needed to receive my tickets, check out the book(s), and get them back to our classroom. Kids started to catch on and charge more for their help but dishing out tens of tickets per book wasn't a problem if I had 100s of shares in that section. Eventually the teacher got wind of how I was making so many tickets and changed how the market worked.
I think some explanation if it is included in a book they wrote on their teaching methods