This method is meant to encourage the "savers" to spend wisely and the "spenders" to save wisely. I'm not sure how well it is working, though.
Nate went to the store with his dad and mysteriously had money to spend on Pokemon cards. When they got home I questioned him and discovered that he had pulled money out of his short term savings envelope and spent it.
"Nate!" I admonished, "What is the base word for 'savings'?"
"Save," he admitted, sheepishly.
"Well, then, why didn't you save it?!?!"
"I DID save it! I saved it up to spend today!"