SAN MATEO, California (WPVI) -- When students got their textbooks at the beginning of the year at San Mateo High School, 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.
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 with 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.
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.
A senior at San Mateo High School, Djelani Phillips-Diop, 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 an 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 within a matter of minutes," said Gelb.
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 followers, checked my followers constantly," said Joshua Cervantes-Solorio, a senior student at San Mateo HS.
Another senior at the school Lea Wadhams said , "You're constantly comparing yourself to other women on your feed, and it definitely takes a toll on your self-image."
Students were asked to write down their daily phone usage before the Yondr pouches.
Many were surprised by their own numbers.
California high school becomes largest public school in the country to ban phones