I think the best way to teach them money saving lessons is by setting it up almost like a game. I know interactive things like that helped me. Maybe something like using monopoly money and setting up a store for things they want with different prices. It could be chewing gum and pencils as the cheapest thing and then an Itunes gift card or a movie (something they would all want) as the more expensive thing in the store. But there should be some good things in the cheaper section to tempt them. This could be a long term thing where they get so much money every week as a salary and a set amount is taken out for rent, groceries, car payment etc. There should also be punishments for not being able to pay their bills and rewards for saving.
That's how I would do it, anyway. I hope this helps.