A local High School (G7-10) has just banned smart phones from their classrooms, France has done a similar thing across the whole country. Many teachers I have spoken to feel this is a good idea. They have seen the effects on younger teenagers. Who are unable to focus for any length of time, anxious and depressed, unable to put the phone in their locker; "Something might happen", "Mum needs to be able to call me", "I need to know - it might be an emergency". I personally witnessed the meltdown in class of a student whose mother had contacted her, during class, to let her know the beloved family dog had been put down.
The social interactions with people outside school take precedence over any learning. These students are anxiety driven and minor disagreements blow up into major incidents.
This is not the majority of students, but a growing minority who are often struggling at school.
Is the solution a total ban? I can see wonderful opportunities for students to use their mobile devices in good productive ways but I do wonder if the immature teenage brain is ready to accept the responsibility of using the device in a constructive manner, I think many see their phones only as entertainment and communication devices rather than for learning, work or organisation.