So, it's nearing Christmas at the end of a long term of school (the last time we had any day off was in early October). In my "weak" Grade 9 group, kids are starting to lose some of their focus. In my mind, I know that they probably cannot help it, because even I am looking forward to vacation. But well, this is the kind of teacher I am. I said this very calmly and firmly to the 9th-graders in the last 10 minutes of class (after they had been idly, overly casually doing work for about 30 minutes):
"Alright, listen. You guys are dismissed today to go to lunch when you have shown me that your worksheet is complete and that everything is correct. ...No, don't complain. You know, I used to do this a lot at my last school, and those kids used to complain to me all the time about being dismissed late, but then the next year those same kids would write me emails to THANK me for teaching them so much math. So, I'll just tell you in advance: 'You are welcome!!'"
The half of the class that had been on task, laughed at this and packed up on time to go. The other half that had to stay late, mostly finished the worksheets within 5 or so minutes of regular dismissal. Only one kid was mumbling angry comments the whole time (but he gets angry pretty easily and I'm pretty used to it and so I don't take it personally), and then everyone else that had to stay late, actually thanked me on their way out. What sweet kids.
Fun fact: Some of my former students in the Bronx used to call me Yangsta or Yangdizzle. No relation to this story, of course. But these kids definitely don't want to be wasting time in my class, lest the real Yangdizzle come out. *wink*