(TNS) — Robert Jessen, the principal at Monte del Sol Charter School, felt as if something was missing from a math class at school he visited last year in Oakland, Calif., to gauge the impact of the Khan Academy math program. But he couldn't quite figure out what it was.

Then he got it: There were no cellphones in sight at Oakland Unity High School.

"The difference was remarkable," Jessen said, "especially during lunch and passing periods. The students were all talking to each other." They paid attention to their teachers, took notes, asked questions and were not distracted during the math lesson."

Oakland Unity administrators put a strict ban on students' electronic devices. The penalty for a first violation: Teachers seize the student's device and the school keeps the device until the end of the school year.

With the backing of the Monte del Sol Governing Board and staff, Jessen initiated a similar ban on electronic devices at the charter school this year. The staff prepared parents and students for the rule last spring. And during registration ahead of the new school year, students signed a technology-use agreement showing they understood the terms of the cellphone ban.

Jessen bought a safe for storing any confiscated items. On Tuesday, the last day of school at Monte del Sol before the Thanksgiving break, he counted 25 devices in the safe. All were for first-time offenses. No one has violated the policy a second time, he said.

Teachers, parents and students say that since the ban went into effect, students are more focused in the classroom. They talk to one another -- and not to their iPhones -- during lunchtime.

Monte del Sol teacher Amy Schroth has noticed the difference. "It's such a relief to have them not be on their phones," she said. "Their faces are looking at you. They are not so consumed at what is happening on their phones. ... We have them back."

Schroth has a son at the school whose phone was confiscated early in the semester. Still, she's a supporter of the ban.

Gabriel Alarcón, who has two ninth-graders at Monte del Sol, said his kids "put more focus on their classes."

His daughter, Victoria, agrees. Most students are adapting, she said. "We get to bond more over lunch and in between class periods. We talk to each other more than we did last year during the day."

Photography teacher Mike Webb gets credit for being the first person to take away a student's cellphone. The boy, a straight-A student, had just pulled out his phone to send a text. "He wasn't even thinking about it," Webb said. "It was automatic, just something we all do."

Webb has mixed feelings about the rule. On one hand, he wants to see educators embrace technology and use it to teach. "That's the world we live in, so we should show them how to use technology and digital devices properly," he said. "We can't pretend it doesn't exist."

But, Webb added, "I like the fact that they can't have a cellphone in class because it is one less distraction."

Not all students like the ban. Arianna Gonzales, a junior, said she finds it "pointless." Since she can't use her cellphone during the school day to check phone messages, texts and emails, she said, she has to do all that when she gets home, and that distracts her from doing homework.

Cellphones and other technology are part of a teen's life, Gonzales said, and students have to learn how to manage them. "If you want to do well in school, you should find your own light, your own motivation," she said. "We should be teaching ourselves self-control, and this is not a way to do that."

Over the past few years, a number of schools and school districts have initiated cellphone bans, arguing that they hamper student learning. A 2015 survey on cellphone policies and their impacts on students, conducted by the University of Texas and Louisiana State University, found that exam scores rose by up to 6 percent in schools that implemented strict bans on cellphones. The ban led to an extra hour a week in instructional time, as well, the study said.

An NEA Today article in 2015 reported that 70 percent of the schools and districts that put bans on cellphones later repealed them for two reasons: They were hard to enforce and many educators, like Webb, felt cellphones and other digital devices could be used to enhance instruction.

Jessen says the ban is permanent at Monte del Sol, and he won't back down.

Cellphone rules at other schools in the city vary.

Santa Fe Preparatory School, for example, only allows high school students to use cellphones during breaks and lunch -- and only to text, not to talk. Jim Leonard, head of the school at Santa Fe Prep, said if a student is using a cellphone in an improper way, a teacher will confiscate it for the day. He estimates his staff collects about five devices a day.

"It's almost like taking an appendage from kids today -- and even adults," Leonard said.

Within Santa Fe Public Schools, each school has different practices, spokesman Jeff Gephart said. "Some secondary schools allow students with cellphones as long as they are off during instruction," he said. "Others allow students to use them during lunch or before and after school. Some elementary schools allow students with fragile needs to use as needed."

It's too early to tell if the ban at Monte del Sol will pay off in test score improvements or extra time-on-task in the classroom, but Jessen believes it will be successful if everyone supports it. "Because we are a smaller school and we know all of our students pretty well," he said, "it's doable. It would be tricky at a larger institution. You'd have to have a huge buildup to it and have complete buy-in by staff."

©2016 The Santa Fe New Mexican (Santa Fe, N.M.), distributed by Tribune Content Agency, LLC.