I think the point is all the "kids are getting damaged by phone use" talking points. It's using the school bans as a useful study; we can see what happens to kids if they're not allowed to use phones here.
iirc a similar study on the Aussie age ban is finding similar results; basically no difference. Some kids benefit, others suffer.
Agree that a study on grades would be useful too
Why would anyone really benefit from just a few hours off their phones?
That's like saying not eating for a few hours makes up for eating 4000 calories at dinner.
Wat? Why would there be a difference? It only takes an hour a day or less of social media with an algorithm designed to make you anxious to really affect your mental health, how would limiting available social media time to 8 hours help?
Isn't it the inverse? i.e we think it is bad for students to have phones in schools, but it might be a problem for the students if we ban them, so let's do the test ... yep, no problem for the students, so let's definitely ban them for educational reasons?