The biggest problem is you get conditioned to instant and constant dopamine hits, which works directly against a lot of the things one is supposed to learn in school.
Kids learn the A-Z in record speed in 1st grade. But they don't learn to concentrate or that learning things can sometimes be challenging and the value of perseverance and that understanding eventually comes.
So in later grades they pay for learning the A-Z too fast through the iPad. Because they didn't learn how to learn.
The net effect in Norwegian classrooms over past 5 years of iPad education seems to be negative and it is not about what kids are exposed to. It is about not learning to concentrate.