(MONEY Magazine) – If you have teenagers, you know how they can make your money disappear. Last year, the nation's 28.5 million adolescents spent nearly $90 billion, according to Teenage Research Unlimited, a Northbrook, Ill. market research firm. To learn how families can help their teens handle money better, contributing writer Echo Montgomery Garrett spoke with Patricia Schiff Estess, co-author of the new book Kids, Money and Values (Betterway Books, $10.95). Highlights:

Q. How can parents get teenagers to listen to money advice? A. The truth is you often won't be able to get them to listen. Money discussions may not be as uncomfortable for you as talking about sex with your kids, but they can be extremely frustrating. Don't preach. Just offer advice from time to time, particularly when spending gets out of hand.

Q. What's the use if they won't listen? A. Because somewhere along the line, when peer pressure isn't so strong, they'll heed your advice. Ultimately, though, teens learn best from your example. If you use money frivolously, chances are excellent that they will too.

Q. What should you try to tell your teen? A. The first step is to communicate openly about your family's financial position -- especially regarding college -- while your teen is still in junior high. If you can afford only a state school, say so. That gives them time to earn money if they want to go somewhere else or to boost their grades to get more financial aid.

Q. What should you do to encourage your teen to save money? A. Help establish a savings goal. For a younger teen, the goal may be a car or CD player; for an older one, college. To buy a $3,000 car as a high school junior, say, a seventh-grader might save $10 a week from allowances and gifts ; in a money-market fund, then increase it to $20 from jobs in high school.

Q. Should you help your teen get a credit card? A. Generally, no. If your child gets a credit card without your cosignature -- and it's pretty easy to do so -- make clear you will not cover the bills, nor will the card issuer expect you to.