California high school goes phone-free, largest public school in the country to do it

SAN MATEO, Calif. -- When students got their textbooks at the beginning of the year at San Mateo High School, in San Mate, California, they also received the Yondr pouch, a locking device for their phones.

The phone slides into it and gets locked through a magnetic device. It's not unlocked again until the final bell rings. The procedure will repeat every day for the rest of the school year.

RELATED: Experiment finds too much social media leads to anxiety in teens

Adam Gelb, the assistant principal ran a pilot project last year with 20 students and decided to do a school-wide, bell to bell program for this school year.

The Yondr pouch is a start-up in San Francisco with a mission to create phone-free spaces, something that resonated with Gelb.

"I really think it's about being present and engaging in the adult that's trying to teach you, your peers that might be in your small group. That's part of the main philosophy that we're trying to preach," he said.

RELATED: Digital Detox Vacation: How it benefits you and your kids

Brad Friedman, another teacher at the school, said he was becoming concerned with excessive use of phones at school. He said he often saw students completely lost on their phones, some not socializing at all with other students.

This week, he's already seeing the difference.

"Everyone else was socializing and eating lunch together, that's what I wasn't seeing enough of when phone usage is at its worst," he said.

Djelani Phillips-Diop, a senior at San Mateo High School, said he definitely panicked at first when he heard he had to lock his phone.

"I panicked, I guess last year when we had phones, I was using it every day," he said.

In case of emergency, every classroom has the unlocking device. Teachers still have access to their own cellphones and landlines.

"We've gotten all 1,700 students unlocked with a matter of minutes," Gelb said.

We spoke to four students who, despite their initial panic, agreed that a phone-free school experience has its benefits.

"I remember sophomore year, I tried to get my followers, checked my followers constantly," said Joshua Cervantes-Solorio, a senior student at San Mateo HS.

"You're constantly comparing yourself to other women on your feed and it definitely takes a toll on your self-image," said Lea Wadhams another senior at SMHS

We even got each student to write down their daily phone usage before the Yondr pouches, even they were surprised at their own numbers. See the video for results.