> But nobody has been able to prove this in any studies, even in ones outside of the school environment.

What do you mean? Here's one published last year:

> This study does not provide evidence to support the use of school policies that prohibit phone use during the school day in their current form, given that no differences were observed in mental, physical, and academic outcomes for adolescents attending schools that permit, versus restrict phone use. However, the negative associations found between increasing time spent on phones/social media and worsened mental health and wellbeing do provide evidence on the need to address phone and social media use in adolescents, and school policies should be developed as part a more holistic approach. [...]

https://www.thelancet.com/journals/lanepe/article/PIIS2666-7...