ENCINITAS, Calif. – Public school yoga instructor Katie Campbell proudly looks out at 23 first-graders as they contain their squirming in a kid-friendly version of the lotus position.

In a voice barely above a whisper, she says into her microphone: “Why look at everyone showing me they’re ready for yoga. A-plus, plus, plus!”

Then the lesson begins with deep breathing and stretches common to many yoga classes. But there is no chanting of “om,” no words spoken in the Indian language of Sanskrit nor talk of “mindfulness” or clasping hands in the prayer position.

Campbell avoids those potential pitfalls for the Encinitas Union School District, which is facing the threat of a lawsuit as it launches what is believed to be the country’s most comprehensive yoga program for a public school system.

Parents opposed to the program say the classes will indoctrinate their children in Eastern religion and are not just for exercise.

It’s a debate public schools across the country are increasingly facing with the rising popularity of the practice and the recent dispute over school prayer.

Yoga is now taught at public schools from the rural mountains of West Virginia to the bustling streets of Brooklyn as a way to ease stress in today’s pressure-packed world where even kindergartners say they feel tense about keeping up with their busy schedules. But most classes are part of an after-school program or are offered only at a few schools or by some teachers in a district.

Encinitas is believed to be the only public school system that will have yoga instructors teach full-time at its nine schools as part of an overall wellness curriculum that includes nutrition and a school garden program, among other things.

“This is 21st-century P.E. for our schools,” said Encinitas Superintendent Timothy B. Baird. “It’s physical. It’s strength-building. It increases flexibility but it also deals with stress reduction and focusing, which kickball doesn’t do.”

The program is expected to teach a 30-minute yoga lesson to roughly 5,000 students twice a week at the district’s schools, which run kindergarten through sixth grade. It is funded with a $533,000 grant from the Jois Foundation, a nonprofit whose board of directors includes the son of the late Indian instructor Krishna Pattabhi Jois, whose teachings are said to have popularized Ashtanga yoga in the Western world and were followed by Madonna and Sting.

Jois Foundation’s program director Russell Case said Encinitas is building a national yoga model for public schools.

“Kids are under a lot of stress. There are a lot of mandates on them to perform. We think it would be extremely helpful to have 10 to 15 minutes possible to sit and be reflective instead of go, go, go,” he said.

Researchers at the University of Virginia and University of San Diego will study the program, including analyzing data on students’ resting heart rates.

They want to know whether public schools can benefit not only children’s learning but also instill in them good eating habits and skills to help their well-being.

The program started in several schools in September but will go districtwide in January after months of protests by a group of parents. Dean Broyles, an attorney, says a parents group he represents is considering suing to halt the program.