A not-surprising finding from a recent study of teenagers has revealed that extra screen time hurts their grades. Specifically, one hour extra each day in front of a screen resulted in a two-grade decline (about 10 points) on exams and two extra hours produced an even greater drop in grades.

Usually these studies don’t allow us to determine causation, but this prospective study, which examined kids over ten years, makes causation pretty clear.

Admittedly, the article didn’t describe what “extra” meant, but I’m going to assume it means above the average amount of screen time or an increase of use over the length of the study.

In another non-surprise, teens who studied or read an extra hour each day performed significantly better on exams than their screen-time counterparts.

Moral of this story: Some screen use is fine, but too much is definitely not a good thing.