Later in the essay, the author has supporting examples AND references for his opening claims. For lowering test scores there are two examples that I found in a few moments of looking.
> In a study of over seven hundred students at West Point, those with computers in class had test scores 0.2 standard deviations below those of students who did not.12
> In one study, the final exam scores of students whose class permitted electronic devices were 5 percentage points lower than those whose classes did not.13
I was talking about the figure claiming to show changes in PISA scores caused by various technologies, for which I can't find the source.
I didn't look closer at the West Point study, but I did read reference 13, which by the way required the use of electronic devices for in-class testing, so it did not actually compare classes permitting electronic devices against those that did not. Rather, it had a proctor remind students to put their devices away when they weren't using them for the lecture.
> In a study of over seven hundred students at West Point, those with computers in class had test scores 0.2 standard deviations below those of students who did not.12
> In one study, the final exam scores of students whose class permitted electronic devices were 5 percentage points lower than those whose classes did not.13