About three years ago I had one particular class so infected with this malady I couldn't take it any more and I removed the clock from the wall. I knew if this was the only move I made that students would begin "inconspicuously" (why do they think we can't see the phones?) checking their cell phone clocks every couple of minutes, transferring their attention from the wall to their laps. So I instituted the timer policy.
I informed the students that I had set a timer to go off one minute before the bell. I told them that once the timer went off I would end class and they could begin cleaning up and getting ready to go, not before. A few students grumbled that one minute is not enough time. So, I set a timer for one minute and we did a "dry run" of how long it took them to put away all of their things and get ready to go. They were all surprised to find that it actually only takes them about 20 seconds to get their belongings in order. I then let them sit there and look at each other for the next 40 seconds so that they could feel just how much time that one minute is. Then I had them get their stuff out again and we held class.
It was amazing. With no clock, the constant glancing and contorting disappeared. Without their anxiety over the possibility of "not having enough time to pack up," they actually paid attention until the end of the hour. Game changer. I have instituted the same policy with every class since that day. When more clean-up time is needed (for sewing classes, project days, etc), I change the timer to compensate.
I use my cell phone for this purpose, as I can set the timers for every class one time, click "weekdays," and never have to worry about forgetting to set them. Every once in a while I do forget to turn them off during Institute Days, and an alarm that sounds like the 108 minutes are up and I need to enter "4 8 15 16 23 42" to prevent the end of the world goes off during an informational session on gangs or library services. Oops, awkward...
When I introduce the procedure to the kids on the first day, I always show one of the students in each class that I have the phone set on "airplane mode" so that they know I'm not also receiving texts : ). This builds their trust, establishes the reason I can have my phone out and they cannot, and keeps me out of trouble.
What kind of trouble can having your phone on during the school day cause? See this article: "Texting Between Classes Can Get You Fired... or Pregnant."
As long as you stick to your word and dependably end class with the timer, the kids are really good about not packing up before time, eliminating that end-of-class clean-up creep. Definite sanity saver!
Anybody else have a system for thwarting the clock watchers?