A few weeks ago, I noticed that a student was surfing the web during my class. So I asked her to come to my office, where she told me – with admirable boldness – that my efforts to police such behavior were wrong-headed. She had grown up with digital technologies, she said, and she had taught herself to “multitask” efficiently. Who was I to presume otherwise?

“Google ‘Clifford Nass,’ ” I replied. “Just not in class.”

Nass, who died last week, was the great slayer of the modern multitasking dragon. A professor of communications at Stanford University, Nass showed that people who did several things at once did all of them worse that those who focused on one thing at a time.

And the more we multitask, he found, the worse we get at multitasking itself. In most human endeavors, practicing an activity makes you better at it. Not so with multitasking: Veteran multitaskers are actually less efficient than people who just started doing it....