A new ritual marks the end of the school day at Brooklyn Technical High School this year. When the metal doors swing open, teenagers reach into their backpacks and rip open the school-issued Velcro pouches that have kept their cellphones out of reach since they arrived in the morning.

The sound of screens coming alive with hours of notifications is sweet relief to students who are struggling to adjust to life under a new state law that forbids smartphones, smartwatches, laptops or other internet-connected devices from bell to bell.

With one million students, New York City Public Schools is the largest district in the country to have banned students from using phones during the school day, although it is part of a growing national and international movement, with many states such as California and Louisiana implementing their own restrictions. Other countries, like China and France, have restricted phones in schools for years.

Since students returned to school in New York City on Thursday, the policy has generated intense debate in the hallways and in many homes, where some parents have expressed concern about not being able to reach their children in an emergency.

“I have a love-hate relationship with it,” said Raisa Ibnat, 16, a senior at Brooklyn Tech. “I do like the fact that my phone is away, and I’m more focused in class.”

But Ms. Ibnat said she was frustrated that she could not use her laptop, as she has for years.

“I don’t like the fact that I can’t do my homework in school, and I can’t take notes,” she said. “And because I have a long commute, now I have to bring, like, five notebooks.”