S.C.
I made it interesting for my son when he was younger by using real money and making a game out of it. Once we'd gone over the values of pennies, dimes, etc., I'd put a bunch of coins in a pile and tell him to show me a particular amount. If he could, he got to keep it. I think knowing he got to keep it motivated him to try and remember. He's 12 now and at the grocery store I have him figure out differences. I'll ask him if it's cheaper by the ounce to buy a larger size box of a particular cereal than the smaller box. He used to assume that bigger was cheaper, but has learned you need to do the math because sometimes you get a better deal buying 2 smaller boxes.