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Study finds smartphone bans in Dutch schools improved focus
(www.reuters.com)
This is a most excellent place for technology news and articles.
You can conclude that teachers experience a better classroom environment. There was also 1/3 that did observe academic improvement.
E: Also, a teachers subjective experience is still an objective result if you are considering the qol aspect of the policy.
I mostly care about longer term impacts. The ban has only been in place for a year and a half, so it's really not much to go on.