Because it wasn't a "smartphone ban". They convinced a group of students to give up their phones completely for 21 days, outside of school too. The reason why

Because it wasn't a "smartphone ban". They convinced a group of students to give up their phones completely for 21 days, outside of school too. The reason why they went to bed sooner is somewhat obvious. It's not something you can replicate as a longer term policy, the students only participated because they knew it was short term and (presumably) they were rewarded for it. And I suspect the effects only work in the short term. You removed their primary source of distraction and they simply wasn't enough time to develop new distraction habits. When I was a teen, I distracted myself from bed with TV, books and the family desktop computer.