No more laptops in Clay Shirky’s classroom:

Over the years, I’ve noticed that when I do have a specific reason to ask everyone to set aside their devices (‘Lids down’, in the parlance of my department), it’s as if someone has let fresh air into the room. The conversation brightens, and more recently, there is a sense of relief from many of the students. Multi-tasking is cognitively exhausting – when we do it by choice, being asked to stop can come as a welcome change.

So this year, I moved from recommending setting aside laptops and phones to requiring it, adding this to the class rules: “Stay focused. (No devices in class, unless the assignment requires it.)” Here’s why I finally switched from ‘allowed unless by request’ to ‘banned unless required’.
Great move by Clay.
I did the same thing with my students when I taught web design at FIT in 2010.
I used to make everyone to put away their phones at the start of class. To back up my request, I’d hold my iPhone up above my head so everyone could see it, and place it face down at the front of the class with the ringer off.
[Because my class was about web design, they were all sitting in front of iMacs with Internet connections, so I’d still have to walk up and down every row to make sure the students weren’t on websites unrelated to their projects.]