Clay Shirky at his best (as usual):
Regarding teaching as a shared struggle changes the nature of the classroom. It’s not me demanding that they focus — its me and them working together to help defend their precious focus against outside distractions. I have a classroom full of riders and elephants, but I’m trying to teach the riders.
He goes on with remarks that are more widely applicable (internal company meetings anyone?):
The structure of a classroom, and especially a seminar room, exhibits the same tension. All present have an incentive for the class to be as engaging as possible; even though engagement often means waiting to speak while listening to other people wrestle with half-formed thoughts, that’s the process by which people get good at managing the clash of ideas. Against that long-term value, however, each member has an incentive to opt out, even if only momentarily. The smallest loss of focus can snowball, the impulse to check WeChat quickly and then put the phone away leading to just one message that needs a reply right now, and then, wait, what happened last night??? (To the people who say “Students have always passed notes in class”, I reply that old-model notes didn’t contain video and couldn’t arrive from anywhere in the world at 10 megabits a second.)
Based on personal experience, I don't really understand why teachers allowed us to use our laptops during class. The amount of students using them to do anything but listening to the class was just overwhelming, especially once wireless connexions became widely available.