Below is Paul Dix's answer to a behaviour question asked by a TES reader. The response was published in the TES:
The Problem
How do I deal with a girl who is constantly smirking? I tell her classmate off, she catches their eye and smirks. I tell the class off, she smirks to other people and smiles sweetly at me. I feel like I am losing. What can I do?
The Expert View:
Resist the urge to "wipe that smile off her face" - it makes you appear as emotionally driven as she is. The power of the smirk elicits a disproportionate response. You need to decide if you want to play the game, or if there are bigger battles to win. You feel as though you are losing; in reality, smirking is a safe way to protest. It would be braver to complain loudly or throw a chair out of the window. Perhaps the smirk is a minor irritant, not a major concern.
Each time you respond emotionally, you confirm that her strategy is working. Each time you refocus attention on the work, compliment her for her smirking ability, ignore it or lighten the response with humour, you take the sting out of it. She will adjust her behaviour when she does not get the reaction she expects.
Arrange a time to talk to her, identify the behaviour that you want her to adjust and reset the boundaries. Explain how she appears to you and to the class. Be honest about the fact that you do not expect her to roll over obediently, but nor do you appreciate her subtle subversion. Her smirk may hide nerves at your "telling off", or be a way to gain creditability with her peer group. If you feel it is appropriate, place her on a class report for six lessons so that you can see if the behaviour has changed.
A radical approach would be "no smirking" signs or "smirking only in designated areas", practising smirking with the class as a brain break or smirking back at her. Make sure that your strategy does not damage efforts to build a positive relationship.
You mentioned "telling the whole class off". It may be worth keeping the behaviour of an individual private - this would take away smirking opportunities and allow you to deal with behaviour without an audience.