Each week, about a dozen youngsters troop into Washington's Children's Hospital to play with the occupational therapists on staff there. Although they appear healthy, their problems lie below the surface.

For some, using a pair of scissors or tying their shoes is an excruciatingly complex ordeal; others find it frightening to jump two inches off the ground; still others cannot tolerate being touched.

These children, and many others who demonstrate the same problems in hospitals and pediatricians' offices around the country, are suffering from a little-known and puzzling disability: sensory integration problems. Simply put, their brains cannot effectively process the information provided by their senses.

It is a developmental problem that occupational therapists have been quietly treating for 30 years, while many medical specialists have ignored it or dismissed the treatment as unproven. Some doctors will not even use the term sensory integration dysfunction, while others are beginning to grapple with the theory as scientists unravel the mysteries of the brain.

"What we're talking about in terms of sensory integration disorders is not one disease or disorder," says Zoe Mailloux, the director of administration and practice at the Ayers Clinic in Torrance, Calif., which specializes in children with sensory problems. "It's really an array of disabilities that relates to how a child can make his or her senses work."

The leading researcher in the field of sensory integration problems, A. Jean Ayers, estimated from her studies over several decades that 5 to 10 percent of American children are affected. Boys are believed to be five times more likely to have such difficulties, said Barbara E. Hanft, an occupational therapist with the American Occupational Therapy Association in Rockville.

The theory defining sensory integration problems was pioneered by Ayers, a California occupational therapist who died in 1988. In most people, thousands of bits of information are constantly being transmitted by the nervous system to the brain, where they are evaluated, acted upon and stored. But for people with sensory integration problems, according to Ayers's theory, there is a breakdown somewhere between the introduction of new information and the brain's reaction to it.

It is unclear where the breakdown occurs, say those who have studied the phenomenon, or why some people have more difficulty with one sense instead of another.

Most research has been conducted by occupational therapists who have focused on behavior and treatment. So far, studies have failed to pinpoint the cause or to determine the number of children who suffer from sensory integration disorders, according to Lynetta Domke, executive director of Sensory Integration International, a nonprofit organization based in California that is dedicated to research and training for occupational therapists.

Researchers suspect there are three primary causes: trauma during pregnancy or birth, such as that linked to drug use or lack of oxygen; a genetic or familial link and unknown environmental factors, Domke said.

"This is not a tangible thing," Domke explained. "You cannot do a CAT scan, and there isn't any scientific evidence of the cause . . . We are at the beginning stages in terms of proving the theory and that the principles of treatment work. Then you work backward to the causes."

The effect of such a disorder, Ayers speculated, is that tasks that should be simple become complex, actions that should be automatic fail to become ingrained. Children with the problem often show uneven development. Ayers found that sensory integration dysfunction is displayed in a variety of ways: delayed speech, clumsiness, hyperactivity, poor muscle tone, aversion to touch.

Since the problem affects some of the nervous system's most basic functions, the body is unable to build upon them, Ayers theorized. For example, a child learning to speak must be able to hear and comprehend words, which requires being able to pay attention to a speaker. He or she must also be able to move the tongue and lips, a complicated task that adults often take for granted. But if a child's brain is not correctly processing information received from the ears, if the child has difficulty concentrating or dislikes the sensation of the tongue moving in the mouth, he or she will be unable to produce simple words.

The disorder does not impair intelligence, but for years children with the problem have been classified by doctors and teachers as slow, retarded or undisciplined. Such a pronouncement has often become a self-fulfilling prophecy, and some children have developed behavioral problems out of frustration.

Most sensory integration treatment offered by occupational therapists and clinics in the area is targeted to children because their nervous systems are believed to develop until age 12. Some adults, however, also seek treatment. Children who do not get treatment often find ways to compensate, but they can still be troubled by new situations.

The problem is often detected when children start school. Those with sensory problems are more prone to have learning disabilities, according to occupational therapists.

"Many of these children have average if not above-average abilities," said Jo Ann DelVecchio, former senior occupational therapist at Children's National Medical Center who now is the rehabilitation therapy supervisor for Children's Home Health Agency. "Perhaps one of the most frustrating aspects is for these kids who have above-average IQs and can't get it out on paper."

Patricia Quinn, a developmental pediatrician in the Washington area, subscribes to much of Ayers's theory. She said that doctors are often ignorant of sensory integration theory and therefore hesitant to recommend occupational therapy.

Occupational therapy for sensory integration problems "is not accepted by the medical community because {many doctors} don't understand many of the theories," she said. "People view it as an alternative therapy . . . {akin to} voodoo."

Nonetheless, Quinn and many occupational therapy experts caution that sensory integration therapy is not a cure-all for learning disabilities. Such therapy can, Quinn said, help children process information and improve their attention spans as well as their motor skills.

For parents, the strain of coping with a child who has sensory problems can be immense. Joan Goodman, an Arlington mother whose 7-year-old son is completing 18 months of occupational therapy, said she realized something was different about her son even though professionals repeatedly dismissed it. "The pediatrician never suggested anything about it, and the preschool teachers suggested he was 'just a boy' " and that his skills were developing slowly, said Goodman.

"He was a very difficult baby. He also became frustrated easily. He's very aware of what other kids can do and what he can do. You just hate to see your child so miserable. I was thrilled to find out {at an occupational therapy screening} that this was something that could be treated."

Sometimes the financial burden compounds the problem of diagnosis; many insurance companies refuse to cover occupational or speech therapy, claiming that no organic cause has been pinpointed for sensory dysfunction.

Elizabeth Stein of Bethesda, who has run a local parents' support group that includes about 160 Washington area families, said she was told by her insurance company that it would pay for her son's treatment if she could prove that the cause of his condition was an accident or illness. But, Stein said, there is no way to determine the cause.

The an annual cost of about $2,000, Stein said, is worth it because occupational and speech therapy have made a major difference in her 5-year-old son Michael's life. Before treatment, he was "almost autistic-like," she said, often hiding from the family under pillows.

One doctor suggested that they seek psychotherapy because "2-year-olds are so emotional," she recalled. Stein and her husband say they thought he was having problems adjusting to the family's move from Illinois.

But after a child psychiatrist and others diagnosed his problems as sensory integration, and Michael began a regimen of occupational, speech and play therapy, he improved dramatically.