On command and slightly out of synch, eight earnest children lunge forward wielding fists.

"Open stance. Now, punch!"

They are kung fu students. Clad in blue acrylic sports pants and white shirts, they line up and face their instructor, Willy Lin.

"Toe out. Good. Now, move !"

Three more times and the younger ones give an exasperated sigh. Eyes roll and one ittle boy stifles a yawn. "Whew!" is heard all around.

During the high kicks, which look like an elementary-school version of a Rockettes show, panic flits across a young face as the girl loses her balance momentarily. Her arms lurch out to avoid stumbling in a back kick.

A little boy picks his nose.

A frown creases one small sweaty brow when a step is left out. Now drawing a complete blank, the boy stops, smiles shyly and begins to giggle.

"I can't do it when my brother does," he complains to Lin."He confuses me."

If having your child learn basic kicks, jabs, blocks and punches makes you fear you may be creating a monster to terrorize classmates or get pulverized sparring with a veteran black belt, don't worry. As taught to kids, these arts are more an exercise in physical and mental concentration than actual fighting. In fact, many instructors say learning such a discipline, now commonly called "martial arts," can be a positive influence on a child's life.

"Pre-adolescent kids are physically and emotionally awkward," says psychologist and t'ai chi instructor Harold Hammond. "Martial arts can help a shy or underdeveloped child really blossom."

James Rhee, tae kwon do instructor at the Jhoon Rhee Institute, says that kids gain self-confidence and discipline through practice. They take on more social responsibility and develop concern for others.

And many instructors prefer teaching children because "it's gratifying to see them get their minds and bodies into shape," according to Gale Janifer of the D.C. Dragons.

Flexible and quick to learn as they are, kids have limited attention spans and are easily bored or distracted. If a class isn't enjoyable and taught like a fast-paced game, you've lost the student. It's important to know when to be strict and when to revert to fun. If it's snowing outside, few teachers can expect unwavering attention. A good instructor needs patience and a creative imagination.

The age requirement for joining classes varies with the trainer. Many prefer to have students be at least eight, while Lin and Rhee will take them as young as five. All say they prefer that a student at least have been away from home before (to nursery school, say) so he's unlikely to panic at meeting new children. And the children should know some basics, such as how to dress thenselves and the difference between left and right.

But most important is that it be the child who wants to learn the sport.

"We have problems with parents who push kids into taking the classes," says John Davis of the Tompkins Karate Association. "We just refund their money and tell them to bring their kid back in six months or a year."

And if you believe the instructors, learning one of these arts is the panacea to the woes of parents and children alike. Hammond regularly recommends that families practice a martial art together because "it acts as a good bonding agent."

One 13-year-old started karate while on the verge of dropping out of school. After five years, he's now a black belt, an honor student and president of the student body.

Of course, most cases are not so remarkable, but "parents say their kids adjust to school more easily and learn better," says Davis. Since many children daydream much of the time, Davis believes that having to focus on movement and balance can help bring them out of their fantasy world for a while.

Every instructor I spoke with insists that children are not taught to terrorize with skill. "We teach them to tone down senseless violence," says Gale Janifer.

"We don't breed bullies," maintains Davis. "Bullies don't have the discipline to stick with it."