An all-out ban on cellphones in schools could improve student performance, according to a new study, but that's not happening in New Jersey. Districts have recognized the devices as tools that can be used for safety and, at times, education.

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In a May 2015 study released by the London School of Economics, students' test scores improved significantly at schools that banned mobile phones. The researchers suggested a phone ban could equate to an extra week of class time over one school year.

Tom Kersting, a faculty member at Indian Hills High School in Bergen County, said electronic devices are definitely having an effect on students' education. Even though they're told not to use their phones in class, it's happening anyway.

"If you're sort of looking at your cellphone while your teacher's lecturing, your brain can't handle two bits of information at once," he said, adding that the hallways in between class periods are packed with kids who have their faces buried in their phones, checking on what they missed over the past 45 minutes.

Schools across the state, at one point, would not allow phones on the premises, period. Over the past several years, though, certain events such as school shootings and terror attacks have prompted districts to change the rules.

Frank Belluscio, deputy executive director of the New Jersey School Boards Association, said schools in the present day generally have policies that allow cellphones. Some handbooks will require that the phones remain in a locker. Others require that the phones be powered down at all times.

"Many policies also extend to various uses of the device," Belluscio said. "For instance, you cannot record things going on in the school, such as a teacher's presentation, or certainly you can't use it in a private area like a locker room."

Belluscio said specific limitations vary from district to district.

Indian Hills' handbook allows students to use electronic devices during their lunch period in the cafeteria; the same goes for Shore Regional High School in West Long Branch. The Bordentown Regional School District "recognizes the usefulness of cellular telephones and other devices as a means of supplementing education under staff supervision." New Brunswick High School tells students that cellphone usage is only permitted "after school."