WASHINGTON — One morning before math, the fourth-graders took a little vacation. To soft music, they walked through woods, climbed a mountain and lifted off with imaginary wings, flying over an ocean, a gentle breeze on their faces. One student saw a school of fish; another spotted a rainbow.

“I see it!” the others piped in, their eyes squeezed tight. “I see it too!”

With the sound of a chime, they were back in their yellow-and-blue school uniforms in a classroom overlooking a blighted neighborhood that has been beset by violence this spring, including two separate slayings of teenage boys at a nearby subway station.

Like a growing number of schools nationwide, Houston Elementary in Washington, D.C., is using mindfulness and other therapies to help children manage the stress they encounter in their daily lives.

Neurological research shows that traumatic experiences such as being abused, witnessing a violent crime or even living in a neighborhood where crime is pervasive can transform the developing brain. They alter the chemical balance, making it more difficult for children to concentrate, create memories and build trusting relationships — all fundamental skills for performing well in school.

The research is motivating educators to rethink zero-tolerance discipline policies that punish kids for outbursts that can be signs of trauma and to rally support for efforts to bring more mental health care into schools, where students and families have ready access to them.

“The brain cannot focus when it's not calm,” said Susan Cole, a Harvard Law School professor and director of the Trauma and Learning Policy Initiative, which advocates for “trauma-sensitive” schools. “Children have to feel safe enough to learn.”

San Francisco has been using a “trauma-sensitive” approach since 2008, including training for students, their parents or caregivers and school staff. This year, Boston received a federal grant to hire trauma specialists to work in 10 public schools.

At a town hall meeting this month, Houston Principal Rembert Seaward asked the students gathered in the cafeteria how many knew someone who had been shot. More than half of the children raised their hands. Anxiety has been running high in the neighborhood in recent months since one teenager was shot and killed at a subway station in northeast D.C. and another was fatally stabbed there two weeks later.

“It's been shooting after shooting after shooting,” said Denise Robinson, a Houston mother.

She tells her second-grade son, Tevin, that the noises outside his window are fireworks, but he hears the sirens and is often anxious and worried about his family's safety.

He doesn't like to go outside and he clings to her when she gets ready to leave, she said. Some days, he resists going to school. “He thinks he's not coming home,” she said.

Excessive stress can have lasting effects. A landmark study in 1998 involving 17,000 adult patients from Kaiser Permanente found that those who had experienced more adversity in childhood, through experiences such as having a parent with mental illness or drug addiction, were far more likely to suffer from poor health later in life, including depression, heart disease, obesity and cancer.

Adverse experiences are common in the general population, with about two-thirds of those surveyed having at least one. But they are far more common in poor neighborhoods.

In an effort to help all families and their children cope, Houston contracted last year with Turnaround for Children, a group that works to make schools more responsive to children affected by trauma.

The organization was founded by Pamela Cantor, a child psychiatrist who conducted a major study about the traumatic effects of the Sept. 11, 2001, terror attacks among students at New York public schools. She found the most profound symptoms of post-traumatic stress were not in the neighborhoods surrounding ground zero, but in the poorest pockets of the city.

“We observed that poverty itself was an adversity in children's lives, a trauma,” Cantor said.

In an initial meeting, Seaward brought a list of 34 students — more than 10 percent of the school's enrollment — who were thought to have acute mental health needs.

This year, Turnaround brought in an outside mental health provider, including an additional social worker who has a full caseload of 20 families.

An instructional coach trained teachers about toxic stress and how the same heart-thumping surge of adrenaline that can save a life also can cause children to lash out at seemingly minor provocations.

In weekly sessions, teachers practiced setting clear expectations and maintaining a calm classroom and demeanor. The goal is to limit disruptions and de-escalate conflicts to give students a chance to learn to calm down.

School suspensions have been reduced significantly in the first year of the partnership, from 76 last year to 19 this year, and a survey showed dramatic improvements in how school staffers perceive the school's climate. Last spring, just a third of employees said they thought students felt physically safe in the building, compared with 94 percent this spring.

Experts say children can recover from adversity, particularly when they have an adult they can trust to help them manage the stress.

At Houston, that person for many children is Darryl Webster, the school's social worker.

Webster has started a grief and trauma counseling group for children who have lost relatives. He also conducts play therapy, which helps children process feelings they have a hard time addressing.

On a recent morning, Webster got a second-grader out of class who was depressed and not talking. They walked upstairs to a room full of toys. The boy picked out a board game, and the two sat on the floor and played until he was relaxed and smiling. Later, the student went to a table stocked with toy figures, and he picked out a pretend hypodermic needle and two cigarettes. He brought them over to the sand table, took out a plastic shovel and buried them in the sand.

Another day, Webster led four squirming little boys toting yoga mats into the library for a meditation session. They giggled at the New Age music on his cellphone, did somersaults and tried to roll themselves up in the mats.

Eight-year-old Tevin was there, the only one who was still and listening as Webster told the group to let go of their worries and fears and concentrate on their breathing.

Webster asked how he was feeling. “Happy,” Tevin said.

He turned his face to the wall and closed his eyes, while Webster continued: “We are on a mountain. It's a beautiful sunny day. Now take out your wings and fly.”