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What happens when a school bans smartphones? A complete transformation | US education | The Guardian
(www.theguardian.com)
This is a most excellent place for technology news and articles.
You actually hit it right in the nail. What actually works is talking to them like thinking, rational human beings, explain the situation and then be a mature adult and understand that they will have to make their own choices and there is nothing you can do about it.
Ideally we should be teaching self-control instead of submission and evasion. A lot of what's going on in the world stems from this tendency.