The Impact of Computer Usage on Academic Performance: Evidence from ... the United States Military Academy

Regardless of the mechanism, our results indicate that students perform worse when personal computing technology is available [in the classroom]. It is quite possible that these harmful effects could be magnified in settings outside of West Point. ...

Comparing our results to value-added estimates of the impact of teacher quality at the highschool level suggests that removing laptops and tablets from a classroom is equivalent to improving the quality of the teacher by more than a standard deviation.
— Susan Payne Carter, Kyle Greenberg, and Michael Walker