One of the most powerful constructions of phrase I have as a management tool is "I need you to...please." Like NYC Educator's colleague's turn of phrase yesterday, notice that it's not a request--it's a very clear, polite command. Lisa Delpit and others have written about how young people from cultures in which it is more common to command children hear questions about behavior as actual questions to which a negative response is acceptable. For example, "Could you please put that phone away?" may very well meet with a negative response and a lack of the desired behavior.
"I need you to put that phone away, please," however, sends a few different messages. It's a command. The "I need you to..." opening says to the student, however, that the command is for a reason, that something they're doing is inhibiting their growth or the learning of those around them, and I need you to help me make this work for everyone can be a powerful message for a young person. And the "please" is important too. I can say this statement in a tone that is not exactly pleasant, but the "please" tells the student that I haven't forgotten my manners or forgotten to treat them respectfully. It doesn't leave a lot of room for argument or complaint. It is now a command that sounds, even to your average recalcitrant teen, like a reasonable request. They may make a face, or mumble "Damn, miss, you beastin'" under their breath while they do it, but they'll do it. And the other 29 kids in the room will notice.
And then add "thank you." I can say "thank you" in the same tone I would say "If you don't stay on task now, I will run your New Era cap through the paper shredder and enjoy it," but it sure is powerful. It's my version of "case closed." We're finished dealing with this issue and I trust that it won't come up again. Moving on.
I learned "I need you to...please" from one of my favorite books on classroom management, Jim Fay's Teaching with Love and Logic. And for more advice on keeping talk (your own) to a minimum with teenagers, read Gary Rubinstein's The Reluctant Disciplinarian.