Desiree McNutt faced the sixth-graders, flicked off the lights and prepared to meditate.

A few feet away, Elkin Rodriguez — her fellow science teacher at George Washington Middle School in Northern Virginia — logged into the classroom computer. He opened YouTube, navigated to Yo-Yo Ma’s rendition of “The Swan.” He pressed play.

For the next three minutes and six seconds, neither adult said a word: The 11- and 12-year-olds knew what to do. Shedding backpacks one recent morning, the students swiveled their chairs toward the front of the room. They rested their hands on their knees. They closed their eyes.

The cello strains faded, and Rodriguez let the silence linger a moment before speaking: “Imagine a voice coming from your heart,” he said. “Repeat it in your mind: ‘There is greatness within myself.’ ”

Minutes later — lights back on, chairs rearranged — the sixth-graders were reviewing for a test on “weather elements” including humidity and precipitation.

What’s happening at George Washington, experts said, is taking place in classrooms nationwide: Over the past five years, “mindfulness” programs have exploded in popularity. In Grand Blanc, Mich., first-graders are breathing to the sound of Tibetan music before class. In Albuquerque, second-graders sniff and speak about raisins before eating them. In Yellow Springs, Ohio, students can choose yoga as an alternative to detention.

Educators hope that leading students in self-reflective exercises such as meditation will give them tools to handle stressful situations, said Amanda Moreno, an associate professor at Erikson Institute, a graduate school that trains professionals in child development. If children can expend less energy to stay calm, the theory holds, they’ll have more gusto for learning.

“It’s meant to help them better attend to what’s happening around them,” Moreno said. “It’s kinda like you slow down to go fast.”

Not everyone is convinced of the benefits — and the rapid expansion of mindfulness activities in schools throughout the country is fueling a backlash from conservative, Christian groups that say exercises such as meditation indoctrinate students in Buddhist or Hindu ideology.

At George Washington Middle School in Alexandria — which enrolls roughly 1,400 students — the meditation sessions were introduced at the start of this school year, the brainchild of McNutt and Rodriguez. The two educators, who teach sixth-grade science to roughly 175 children in total, said results were swift.

“You can see the change in the kids: They cool down, they relax, and they’re just a little bit more open to learning,” Rodriguez said.

“They’re just kinder kids,” McNutt said.

Post-meditation, McNutt said, her students offer to help one another with assignments unprompted, tease their peers less and say “please” and “thank you” more often. Some now request good-morning hugs.

Early research is promising. Last year, Harvard education professor Martin West conducted a study of Boston sixth-graders, asking 50 to sit for a 45-minute mindfulness session — which included meditation and other “relaxation exercises,” he said — at the end of the school day four times a week. He asked another group of 50 children to spend that time studying computer coding.

After eight weeks, West found that students who underwent the mindfulness training reported “a substantial reduction in perceived stress” as compared with the students immersed in their computers. West said the result was supported by brain scans: Children in the mindfulness group also showed “reduced activation” in the portion of the brain associated with stress response.

“The next step is seeing whether this translates into meaningful academic gains for students,” West said.

George Washington’s principal, Jesse Mazur, said he will assess at the end of the school year whether sixth-graders taught by McNutt and Rodriguez have made unusually strong academic progress compared with their classmates.

Even if they haven’t, Mazur said, he believes meditation is worthwhile. He is encouraging more teachers at the middle school to follow McNutt and Rodriguez’s example. The principal is a strong believer in the benefits of “being mindful,” he said, a lifestyle he discovered through his wife, who teaches health and wellness at a Virginia private school.

Mazur’s family began pursuing activities such as “gratitude journaling” at home several years back. About 18 months ago, he decided to bring the philosophy to work. Four times a year, he closes his weekly email to teachers with a few suggestions: Have you considered breathing exercises? Asking angry children to enter “their calm space?” What about chair yoga?

“Students need a moment of respite from the day,” Mazur said. “I’ve seen it again and again: They emerge ready to learn, frankly grateful for the opportunity.”

McNutt and Rodriguez knew they could count on their principal’s support but decided on their own to start the meditation program. Rodriguez, a lifelong meditator, first tried guided meditation four years ago with a handful of eighth-graders. It took him until this year to persuade McNutt.

“Now, it helps me, too,” said McNutt, who has begun meditating outside of school three or four times a week. “I see my kids, and I hear them, in ways that I never did before.”

Some sixth-graders were skeptical, worried that meditating would make them appear “uncool.” So McNutt and Rodriguez played videos of celebrities such as LeBron James meditating, and students’ fears subsided.

Only two children have declined to participate, Rodriguez said. During meditation sessions, he allows the pair to sit quietly in the back of the room, eyes open. Otherwise, McNutt and Rodriguez said, they have encountered little resistance.

Candy Gunther Brown, a professor of religious studies at Indiana University at Bloomington, warned that may change. Over the past five years or so, she said, some Christian, conservative groups have begun speaking out against practices such as meditation in schools. These activists argue mindfulness programs violate the constitutionally mandated separation of church and state, Brown said, because they expose students to Buddhist or Hindu ideologies.

Legally, the question is unresolved.

“The Supreme Court has just about exclusively dealt with Christian practices like prayer and Bible reading in schools,” Brown said. “There’s not been any cases on a practice like yoga.”

The American Center for Law and Justice, a Christian advocacy group, is keeping a close eye on mindfulness initiatives in schools, said senior litigation counsel Abigail Southerland. The center became aware of the issue after parents throughout the country contacted the group with concerns, she said.

Southerland said programs similar to George Washington’s are especially troubling because it can be difficult for students to opt out. Brown noted these kinds of initiatives are ripe for a legal challenge.

“There’s a difference between teaching a student about various religions and leading them in religious practices,” Southerland said. “Here, you have a captive audience.”

Alexandria sixth-grader Lara Elise Forbes, 11, began suffering from anxiety shortly after starting middle school. Soon, she was struggling to keep her breakfast down, overwhelmed by worries about her report card, test scores and assignments.

It got so bad that Lara and her parents visited a doctor, who prescribed anti-nausea pills. Those helped — but nothing was so effective as the five minutes of meditation in McNutt’s science class.

“It’s kinda hard to stop thinking about everything, at first,” Lara said. “Then you feel so much better, and you can just really focus.”

She no longer feels nauseated in the morning. When she gets stressed at home — sitting down to face mounds of homework — Lara turns off the lights in her bedroom, perches on the end of the bed and clears her mind. Sometimes, she plays Yo-Yo Ma.

A few weeks ago, Lara tried to persuade her sister, a seventh-grader, to sit in silence with her.

“She didn’t really listen to me,” Lara said. “And too bad. She never gets any of her homework done.”