Q. "Our daughter is 14 years old and starting high school. We have been thinking of giving her a monthly clothing allotment.

"Her preference in clothes runs to the classic styles, so there is no problem there. Recently we gave her our charge card for one day and she brought home one pair of pleated brown slacks, a dressy beige blouse with lace at the collar, a brown plaid skirt and a tan crewneck sweater ($75 total at Sears), so we know that she knows what she's doing.

"Our problem is trying to figure out how much to give her each month and what to expect her to buy with it. For example, should a winter coat as well as underwear and hose be included? I think for large purchases, such as a coat, she would have to 'save' her allotment for a few months.

"Could you also say a few words about the clearance racks and end-of-season sales? She just sails right by them, while that is the first place I stop.

"We also would like your opinion and/or advice about the 'charm/fashion' advisory boards at some department stores for teen-agers. She could use instruction in posture and carriage. She insists she cannot breahte when I tell her to pull her stomach in; I can, but don't know how to tell her to do it."

A. As a parent, the idea of a clothing allowance is one of the best we've ever heard of, but it has one drawback. We've never seen it work.

No doubt it has, somewhere, sometime, but it hasn't for us, or for anyone we've ever known who has tried it, so we've decided it must be one of those pat ideas concocted by Seventeen or the glossy women's magazines. It's only practical on paper.

If you do try it, remember that a clothing allowance is given to teach a child how to handle money, not a credit card. It takes cash to help a child realize that money and work go together. There is no such thing as a hard-earned credit card.

A card for one store is a bad idea, too. Your daughter only learns to shop wisely if she can go from store to store to compare prices, styles and quality, That's why we think every young teenager should do a certain amount of shopping at the fanciest stores in town -- Bloomingdale's, Garfinckel's, I. Magnin, Neiman-Marcus, Lord and Taylor and Saks, etc.

The clothes sold in these stores will give her a yardstick for quality to measure all fashion by and she may be able to afford some of them, too, particularly if she shops in the pre-teen department. The top size often fits well, looks great and costs less.

These stores always have a reduced rack in every department, and because they usually have the latest styles first, they put them on sale first. And, until your daughter learns to check the sales first, she's not as mature as you think.

She also should go to some of the zingier thrift shops -- like the Junior League shop on M Street NW, or Classic Clothing, both in Georgetown and on Benning Road NE -- which have first-class hand-me-downs. A teen-ager is old enough to learn that pride has no place in a pocketbook.

Although we don't think it's a good idea to give a monthly clothing allowance, we do think you daughter should know approximately how much the family can afford for her to spend on clothes -- including underwear and a winter coat -- and shoes. This doesn't include the pantyhose or mittens you might pick up for her at the supermarket, even if you know she needs them. She's the only one who has access to her clothes money.

She can draw on this set amount as the needs -- and the sales -- arise, but if she spends it six months early, she'll have to babysit enough to buy the rest. To keep her expenses tallied, she should have a ledger to record her expenses so you (and she) can know where the money has gone.

Before your daughter does any more shopping, however, she needs to go through her clothes, keeping to one side those she likes and that are in good condition. With your help she should repair the rest, even if she doesn't like them, or they're outgrown, so they can be given away. Your daughter not only is learning to care for herself, but for those who have less.

The list of the clothes and shoes she keeps is written in the ledger, too -- an inventory to show what she needs. This stops a lot of impulse buying, which is an easy trap after the first few careful shops.

And for one last shopping tip: There is much shoplifting these days and teen-agers often are suspected -- and harassed -- when they shop alone. That's why she should leave a shopping bag at home and dress as conservatively as possible. There's no point in turning an exciting adventure into an embarrassment.

As for the charm schools and advisory boards -- don't bother. They put such an emphasis on clothes that it's hard for a young teen-ager to remember that they're not as important as she is.

For posture, take your daughter to the doctor. Many children at 11 or older -- especially girls -- get scoliosis, a side-to-side curvature of the spine. If it's more than 10 degrees, and if the child is still growing, it needs treatment.

If her spine is all right, she'll learn to tighten and tuck in her seat so her stomach automatically stays flat, but she won't do this until she's ready to grow up. That's when she will learn from those glossy magazines, or from classes in aerobics or ballet, where grace and carriage are part of a larger goal.

To make an issue of her posture will only put distance between you, for a child is sure to figure -- rightly so -- that the way she walks after 14 years is pretty much her own business.