The approach of school can be an anxious time for any child, but it's especially difficult for those like Daniel McKenna.

A normal, talkative 6-year-old at home, Daniel spoke only once to his kindergarten teacher last year. Toward the end of school, he told her his cat had had kittens. He even told her how many, and their colors. But that was it.

Daniel, who lives in Sharon Hill, has an unusual - and, until recently, largely untreated - psychological disorder called selective mutism. In an extreme reaction to anxiety, children with SM are unable to speak in certain situations - often it's school - but usually are fine with family or friends.

"If you would see him in school, he just totally shuts down," said Daniel's mother, Marikate McKenna. "He just looks scared to death. He keeps his hands in his pockets and he won't speak to anybody... . It was hard for him to even get out of his seat to go to the rug for story hour. He just freezes."

Yet when he's in his "comfort zone" at home, she said, "you would never think that there was something wrong with him."

She is still talking with her school district in Delaware County about how to make the coming year easier for Daniel.

Elisa Shipon-Blum, a family physician from Meadowbrook, gave up her practice in Northeast Philadelphia to focus on selective mutism after her daughter, now 8, developed it. The girl is fine now, but Shipon-Blum, who is not a therapist but did extra residency training in children's mood disorders, devotes her time to counseling children with selective mutism and their parents, including the McKennas.

She is executive director of the Selective Mutism Group - Child Anxiety Network, an education, research and support organization. Although its roots go back a decade, it has seen its greatest growth in the last three years.

"These kids literally suffer in silence," Shipon-Blum said. Left untreated, the disorder can compound psychological problems because children grow more isolated and fail to develop normal social skills. Even without treatment, however, few people above the age of 16 to 18 remain selectively mute.

Estimates of the prevalence of SM vary widely. A UCLA study published this month found that seven of every 1,000 students in kindergarten through second grade in a Los Angeles school district had the disorder.

Selective mutism was once known as elective mutism and was often considered defiant behavior. In the last decade, experts changed the name and have come to see it primarily as an outgrowth of anxiety or social phobia.

But many teachers and counselors, even psychiatrists, continue to treat children with the disorder as being controlling and manipulative, Shipon-Blum said. It is true, she said, that some children become defiant, but that is a reaction to their frustration with their inability to speak.

The condition is also often mistaken for autism, a much more serious problem.

On the other hand, many pediatricians and therapists tell patents not to worry, because so many children can be shy and quiet early in a school year. The mutism has to persist for more than a month for the diagnosis to be made.

Shipon-Blum says selective mutism is a "pathological form of shyness." In social settings, children with the disorder have a characteristic look: statuelike, their faces frozen and expressionless.

"These children are not choosing or refusing. They cannot [speak]," she said. She believes they may be so paralyzed by fear that they are physically unable to speak. Many say the words got stuck in their throat.

Deborah Beidel, a University of Maryland psychologist and codirector of the Maryland Center for Anxiety Disorders, said no studies had been done on whether children with selective mutism are unable to speak. But, she said, they are no more anxious than other children with social phobia who, despite their fears, are able to speak in social settings.

She believes they've learned to deal with their anxiety by becoming mute.

Shipon-Blum, who says she has seen about 500 selectively mute children in the last three years, said they tend to share certain traits. Most have social anxiety. They also often have shy-bladder syndrome (inability to urinate in public places), and many are very picky eaters; some refuse to eat in front of strangers. At home, they may be stubborn and bossy.

While many are socially crippled by the disorder, others are quite functional. Emily Mallon, for example, a 12-year-old from Downingtown, has never spoken to a teacher in class. Yet she gets good grades. She's on soccer and basketball teams. She plays flute in the band. In fifth grade, she got on stage and did a dance with a friend.

"Some of these kids, they want to be recognized. They want to be a shining star," said Gina Mallon, Emily's mother. "They want attention. They just can't talk."

Approaches to helping children with SM vary, but the goal is to help them feel less anxious and to make small, incremental behavioral changes. For some, it may be an improvement to nod or even to tap once for yes and twice for no. But they need to continually progress toward speaking publicly. Sometimes, medications such as Prozac help.

Shipon-Blum counsels parents to make school less threatening. Children should meet their teachers before school starts and become familiar with the classroom, she said. Parents should schedule lots of one-on-one play dates. Parents may have to visit school often, talking with the child during lunch or after school in the classroom, so that the child gets used to talking in the building.

Children also are encouraged to communicate with teachers in other ways. Some write notes in class. Emily Mallon e-mails teachers. This year, her mother wants her to begin calling teachers' answering machines.

Shipon-Blum says schools need to make allowances for children with selective mutism. They may need to tape oral reports at home. Teachers should not try to force them to talk.

"The school allows me to pick kids to be in her class each year," said Sherry Heckman, of Muncy, Pa., whose 8-year-old daughter, Kayla, is now able to speak with her teacher but hasn't been able to talk in front of the whole class. "I get to pick out her teacher each year."

Nathan Blum, a developmental pediatrician at Children's Hospital of Philadelphia, believes that SM is sometimes the result of a specific phobia about talking. He suggests small rewards for small changes. "We try to find the smallest first step the child can make," he said. That might be as simple as answering "yes" when a parent, who has come to the classroom, asks, "Do you want to go get an ice cream?"

Beidel says it's important to work on reducing anxiety, but she does not believe that's the key to getting children to speak. Mutism can become an ingrained way of coping with anxiety, she said, and is reinforced by parents or friends who speak for the child.

"We look at what's maintaining the behavior," she said. "What's maintaining the behavior is sometimes very different from what initiates the behavior." Her rule: "No one anymore can communicate for the child." The child can communicate through notes or gestures, but only attempts to speak, no matter how small, will be rewarded.

After years of mutism, some children have told her they're worried about the attention that talking will bring.

She told of one little boy who spoke for the first time after months of silence in his classroom. His teacher screamed and hugged him.

He didn't talk for another year.