When Jim Shackelford bought his daughter Leslie her first pair of ice skates six years ago, he followed his instincts on children's footwear to their seemingly logical conclusion. "We said, 'Gee, her feet grow so fast we'd better get the skates a size too big,'" he recalled. "So we bought her the very, very cheapest, oversized skates we could find. She could almost turn around in them without moving.

"Somebody finally took us aside and said, 'For God's sake take those things off her or she'll never get anywhere.' It took us over a year to learn that if the kid is gonna skate, a good fit is mandatory for skating progress."

Shackelford's reasoning is repeated every winter by countless well-meaning but inexperienced parents, and it's the No. 1 reason kids can't skate well, according to skating instructors, manufacturers and club officials.

"In no sport is the equipment more critical than in skating," says Florence Siffered, figure test chairman of the Washington Figure Skating Club. "The fit for skating boots is more demanding than for ski boots. If they don't fit tightly, the child's feet will turn and they'll cry and think they can't do it."

Simply put, boots that are too loose, let your feet slip. You'll get blisters, and you'll lose the feel of what you're doing on the ice surface.

But don't think that just because your toes are up against the front of the boot, you've got a good fit. That's too easy. "Toes aren't the real citerion," says Mike Cunningham, manager of the Village House Ice Rink in Falls Church. "We fit by the ball of the foot. Ideally, you want to have the heel locked down in the boot - that's what gives you the control."

The quality of the boot is also important. If you want to learn to skate well enough to do basic spins and jumps, you ankles should have the support of a good pair of leather boots.

Many people don't know this, and think they can't skate because they've got weak ankles. "Well, there's no such thing as weak ankles," says Dick Schichting, vice president of Reidell Shoes, Inc., a skating boot manufacturing company in Red Wing, Minnesota. "With the strength we have in various kinds of boots, you can get a boot that will support your ankles."

Another mistake, and one that also affects the boot's support, is wearing two or three pairs of thick socks. "I shudder when I see kids come into public skating sessions and put on a couple pairs of very heavy sweat socks," Shackelford says. "Right away their ankles turn and there's no support at all. A thin sock means the boot can give you as much support as necessary. Maximum support would be going to no socks at all."

Since good skates are expensive - you can count on shelling out $40 to $50 for a good pair of boots and blades - many parents are tempted to start their kids out with an inexpensive pair. This way, you can find out if they like skating before you invest in a better pair, right? Wrong. "Of course they won't like it," says Cunningham. "They can't stand up in them!"

Shackelford agrees that "There's no way on God's green earth you can learn to skate with boots that chep. But every year, right after Christmas, there they all are wearing these pieces of cheap vinjl, and their ankles are right on the ice."

Another reason to wear leather boots is that leather's porous, and lets your feet "breathe." Your feet won't sweat, and you won't get skin rashes as you can wearing non-porous vinyl boots.

If these arguments don't cut any ice with you, there's another reason to invest in good-quality skates: their resale value. When the kid has to have a larger size, which is inevitable, you're better off selling a leather skate than one with man-made material. "At a reduced rate, a used skate is a good buy for somebody else," Shackelford says. "A really good skate has a residual value, just like an automobile."

He should know. After his daughter Leslie advanced to the point where her skates were averaging $200 a pair, he became active in the Washington Figure Skating Club's skate exchange, where parents save money by recycling the expensive skates their kids regularly outgrow. Leslie Shackelford's first good pair of skates had been custon-made in Austria for someone else; by the time they arrived, the person for whom they were intended had already outgrown them, and Leslie was able to get them for half-price.

If you're not a member of a skating club, a bulletin board at the nearest rink is a good place to find used skates. In most cases, the skates listed will have been bought at a rink, and will usually be of better quality than you could get at, say, a garage sale.

Mike Cunningham offers another money-saving tip: If you can't afford to buy good skates, even used half-price ones, use rental skates. "I'd much rather see a kid in a pair of rental skates than cheap ones," he says, because they're leather, there's a wider variety of sizes, and there is someone at the rink who can fit them properly.