After one teacher at San Lorenzo High School brought pouches, created by the tech start-up Yondr, into her classroom to lock away students’ phones, the entire school began using them from the beginning of the school day at 8 a.m. until the end of the day at 3:10 p.m.

According to a 2018 study from the Pew Research Center, more than half of teens said they felt loneliness, anxiety, or upset in the absence of a cellphone. The study also found that girls were more likely to feel these sentiments than boys.

“If something feels weird about modern life to young kids who are dealing with a lot of angst and anxiety in general, maybe it has something to do with relating to the world primarily through a screen eight hours a day,” Yondr’s founder Graham Dugoni told CNBC.

Students said they initially felt awkward and annoyed having their phones taken away during the school day, but added that they started to see more teens interacting with each other. One student added that not having a phone in class helped with concentration.

In an interview with Wired, Dugoni described attachment to phones as physical. “It’s much more a body thing, so it was always clear to me that whatever solution there is to this problem had to be itself physical and tangible.” He added that because it’s such a physical impulse to frequently check a cellphone, that “it’s going to affect your nervous system and your patterns of thought and social interaction.”

The pouches are now being used in thousands of schools in the U.S., Canada, and Europe at an annual cost of $15 to $30 per student, depending on the size of the school, according to CNBC.