SCREEN TIME: Teens are on phones for 70 minutes at school, 300 minutes a day overall.

Teenagers spend 70 minutes of the school day on their phones — nearly all on social media, video and gaming apps — according to a recent study, report Lauraine Langreo and Gina Tomko in Education Week. The average school day is 400 to 500 minutes.

The data came from teens who participated in the nationwide Adolescent Brain Cognitive Development (ABCD) Study, and agreed to install a tracking app on their phones.

Students rarely used their smartphones for education or productivity apps, said lead researcher Jason Nagata, a University of California, San Francisco pediatrics professor. While some were on their phones during lunch or other breaks, rather than class time, that’s troubling too, he said. “It’s important that kids, during breaks, have time to rest, to have face-to-face social interactions with their peers, and also just be outdoors and physically active.”

Overall, teenagers spend about five hours a day — 300 minutes — on smartphones, with nearly two hours of that on social media, researchers concluded. That doesn’t leave much time for an after-school job, sports, a hobby or just hanging out with friends.

This is exactly what the phone’s parental controls are for. Kids hate them, but that’s the point.