The remarkable thing about all the fuss is that, until now, there hasn’t been really great data on how classroom computing affects learning. There have been some small-scale, short-term experiments. A 2003 study found that laptops make it harder for students to remember what they had just learned in lecture. A 2014 study showed that students are less likely to understand complex ideas when they are forced to take notes by computer instead of by hand. But these were all contrived situations involving immediate recall. It’s less clear how laptop use affects students over the course of a semester.

Now there is an answer, thanks to a big, new experiment from economists at West Point, who randomly banned computers from some sections of a popular economics course this past year at the military academy. One-third of the sections could use laptops or tablets to take notes during lecture; one-third could use tablets, but only to look at class materials; and one-third were prohibited from using any technology.

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Unsurprisingly, the students who were allowed to use laptops — and 80 percent of them did — scored worse on the final exam. What’s interesting is that the smartest students seemed to be harmed the most.

Among students with high ACT scores, those in the laptop-friendly sections performed significantly worse than their counterparts in the no-technology sections. In contrast, there wasn’t much of a difference between students with low ACT scores — those who were allowed to use laptops did just as well as those who couldn’t. (The same pattern held true when researchers looked at students with high and low GPAs.)

These results are a bit strange. We might have expected the smartest students to have used their laptops prudently. Instead, they became technology’s biggest victims. Perhaps hubris played a role. The smarter students may have overestimated their ability to multitask. Or the top students might have had the most to gain by paying attention in class.

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The size of the laptop disadvantage was modest. The average score on the final was 72 out of 100, and students in sections with laptops scored about 1.7 points lower. But it’s hard to understand what 1.7 points means without knowing how bunched up or far apart people’s test scores were. (For the stats-savvy, the effect size was about 0.2 standard deviations.)

So here’s another way to think about it. The average score on the math section of the SAT last year was 511 out of 800. The difference between exam grades in the laptop-friendly sections and exam grades in the no-laptop sections is equivalent to the difference between scoring a 511 and scoring a 491 on the SAT’s math section. (That’s roughly the same boost a high school student might expect from hiring an SAT tutor.)

The researchers — Susan Payne Carter, Kyle Greenberg and Michael Walker — were also surprised to find that the tablet-only sections did just as poorly as the laptop-friendly sections. Even though students were not allowed to check email or play games on the tablets, the technology still seemed to interfere with their learning.

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Still, these results are probably on the optimistic side. At West Point, sections are capped at 18 students, so the instructors could easily call out people who were obviously goofing off on their laptops. The problem of computer distraction is probably much more severe at other colleges, where lectures might hold hundreds of students.