TriIt’s basketball season, and your son has news for you: He needs a pair of $120 Adidas T-Mac sneakers, or he just won’t be keeping up with the Joneses. Oh yeah — while you’re at it, Mom, can you throw in one of those new Nintendos? They only cost a cool $250, after all.

If you’ve heard requests like these, or even comparatively cheaper pleas from a younger child, it may be time for a lesson in relative value.

Relative value, one of the most important educational concepts in my financial literacy curriculum, is the cornerstone of teaching responsible financial management. The idea is simple: You help your children grasp the “real” cost of an item by teaching them to consider how much work they’d have to do, or what they’d have to give up, to pay for it.

As an example, a trip for a family of four to Disney World for a week might cost, say, $6,000. That number may be too abstract to mean much to a child. It’s easier to understand that the vacation cost Mommy and Daddy two weeks (or four, or eight) of work — and that for a child with a weekly allowance of $8, the trip represents more than 14 years’ worth of income.

This approach works even better with smaller expenses, and can be used to make your child’s (and your own) purchasing decisions much clearer. Take those $120 sneakers. It really puts things in perspective for a child to learn that he’s welcome to buy the sneakers he pines for, so long as he is willing to save his entire allowance each week for three months.

For an older child, a useful approach is to put the purchase in terms of labor. How many lawns will Jenny or Johnny have to cut to pay for that new video game? Five lawns? Ten? The idea of cutting 10 lawns to earn enough money for a computer game helps a kid decide — almost instantly — whether he or she really wants the item.

You can use the powerful tool of relative value in other ways, too. One useful method is to teach your child to think about what other purchases she is forgoing when she decides to buy something. For example, that $6,000 vacation would be fun, but it also might represent one-third of the price of a new car. Put the vacation on hold for a year or two, and the family is a step closer to getting rid of that old station wagon that makes the kids duck as you drive through town.

To help reinforce the concept of relative value, I’ve created a teaching game based on the popular TV game show “The Price Is Right.” You’ll need some pictures of products, cut from magazines and newspapers, a pencil and pad for each player, and a moderator or judge — a great job for you.

The game starts with the moderator holding up a picture of a product and asking each contestant to guess the price in terms of relative value, for example, how many weeks’ allowance the product sells for or how many extra jobs, like baby-sitting or yard work, would go into paying for it. The winner is determined after all guesses are collected. The player who estimates the value closest to the actual cost, without exceeding it, wins.

When your children understand the relative value of a product or service, they can begin to make informed decisions about whether or not springing for it is a wise use of their money. And you can use the concept of relative value not just to help your child set priorities, but also to understand yours. That $250 Nintendo isn’t just 20 lawn-mowing jobs; it’s also enough money to fill Dad’s gas tank six times. Spend the money on the game system, and the money to fill the tank has to come from somewhere else.

Be creative. Continue explaining relative value to your children in different ways. Your goal is to encourage them to get into the habit of asking, “What will this cost me in time or labor?” Eventually, it will begin to sink in.