“It’s a phobia that’s as real as someone who’s afraid of heights,’’ Ray said. “You can’t make someone like that climb a tall ladder and just stand there and, quote-unquote, be normal.’’

Ray compares selective mutism to phobias when she explains her son’s diagnosis to people who haven’t heard of it. It was once called “elective mutism’’ in the Diagnostic and Statistical Manual of Mental Disorders, the psychiatrists’ catalog of mental illnesses, implying children had a choice in the matter.

It can be challenging to tease out what is typical and what is problematic, Van der Feen said. After all, anxiety and worry are part of normal development. Toddlers are afraid of monsters and preschoolers fear being separated from their parents. Some children are temperamentally shy. But the question becomes: Are they making friends? Are they still afraid of the dark when peers aren’t?

“Anxiety disorders are very common in childhood and adolescence and they are very often undetected or untreated,’’ Dr. Julie Van der Feen of McLean Hospital said. “There is increasing evidence that early identification and treatment reduce the impact of child anxiety on children’s relationships, their academic functioning, and their social functioning.’’

Early recognition of selective mutism and other anxiety disorders can be crucial, specialists say. Age-appropriate therapy for child anxiety disorders has an encouraging success rate of 70 percent, research has shown.

That moment started Ray and her son on a search that eventually led to a diagnosis of selective mutism, a relatively rare anxiety disorder that affects an estimated 0.5 to 0.75 percent of the population. Children like Ray’s now 9-year-old son — whose name she declined to disclose because of the stigma that clings to such problems — can be chatterboxes at home, but they do not speak in other settings such as school, their neighborhoods, or the grocery store. They may develop other ways to communicate, through nods, gestures, or whispers to trusted teachers or peers, but their inability to fully participate in communications can lead to academic and emotional problems in childhood and in some cases set the stage for depression and social isolation later in life.

“They said he doesn’t know his ABCs and he can’t count to 10. We were shocked,’’ Ray said in a recent interview. When she told his teachers he talked nonstop at home, they said, “He has never spoken to us.’’

Despite Ray’s misgivings, nothing prepared her for the first parent-teacher conference when her son was 3 1/2.

Jennipher Ray knew her son was on the quiet side. Even as a baby, he was nervous, and as he grew older his body would stiffen when he crossed the threshold into his day-care center near his mother’s part-time job in downtown Boston. His pediatrician said he was “just shy’’ and would outgrow it.

It’s unclear what causes selective mutism. Jami Furr of the Center for Anxiety and Related Disorders at Boston University says when children with selective mutism have parents or grandparents with a history of shyness, social anxiety, or depression, that suggests a genetic vulnerability. Environment may also play a role.

“Often if parents are also more inhibited and show anxiety, they are going to model those different behaviors and perpetuate the problem,’’ Furr said. This makes children less likely to go out and approach the world.

But parents’ behavior is not always a factor. Before a child is diagnosed with selective mutism, neurological causes, developmental delays, and communication disorders are also considered. Selective mutism can occur alone or with other disorders. Specialists advise waiting a month after a child has begun school or entered another new setting before doing any testing.

“All kids have an adjustment period. They may be a little shy in the beginning and then they warm up to the situation,’’ Furr said. Later “we look at the level of impairment, across different contexts within the school and community to see if it’s at the level of a disorder.’’

Children with selective mutism may not lag behind in their development or intelligence, Furr said, but they can suffer socially, especially as they get older. Younger children can be remarkably empathetic, willing to help out or take at face value that their classmate doesn’t talk. But come middle school, tolerance can evaporate. The more anxious children become about being different, the more likely they are to withdraw. In general, untreated anxiety disorders are linked to higher rates of depression and substance abuse as young people reach their 20s.

Treatment for selective mutism combines behavioral strategies and cognitive behavioral therapy, which encourages changes in how to think about anxiety-causing situations. New people might be “faded in’’ during a therapy session, meaning a new person would sit or stand outside the door while the child and parent talk, eventually coming closer until that person enters the child’s speaking circle. Parents might fade out, too, as the child becomes more comfortable. In school, a child might first read aloud in a classroom with the therapist, and then eventually with the teacher, then the teacher and a peer and then several peers, slowly building confidence.

Older children are encouraged to examine their anxious thoughts about speaking up, working through their fears of the worst that could happen. Some children with severe anxiety are given medications such as Prozac, but most go through behavioral therapy to see if it works first, BU’s Furr said.

Depending on the child, seven months to a year of behavioral therapy can lead to full remission of the disorder, she said. The longest follow-up to date is seven years and the results are hopeful for children who learn how to speak up.

“Once they make that leap and cross that barrier, typically you start to see them perform extremely well in a variety of settings,’’ Furr said.

Just ask Jennipher Ray.

Her son, now in fourth grade, is no longer in therapy, which at the end included trips to a busy Barnes & Noble bookstore, where he had to ask a salesperson for directions to the restroom. He is confident enough now to speak up in restaurants if he wants another beverage, and has learned to deal with situations that cause angst. That’s when he uses a tool from cognitive behavioral therapy, thinking about how high on a “staircase’’ his fears have climbed so he can manage a way to respond to them.

In carpools, Ray has heard his friends ask if he remembers being back in first grade when he didn’t talk. She said he wonders himself why he didn’t speak, telling her how much easier it would have been if he had.

She remembers the second week of second grade. She got an e-mail message from his school saying she would be proud of what he had done that day. When she went to pick him up, she heard why.

“He got up in front of the whole school and he used a loud voice to share a project at an all-school meeting,’’ she said. “The assistant headmaster saw me, gave me a hug, and we all cried. . . . He’s just come so much further than we thought.’’

Elizabeth Cooney can be reached at ecooney@globe.com.

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