@jvargas : Yes I have a skip in my walk when I encourage someone through my struggles in life.

I would first of all, use proximity to be subtle in my discipline. Then I would adress them 1 on 1. Then I would ask them in front of class to refrain from talking or I will make seating changes. Then I will stop teaching and wait for them to stop interrupting. I would document and eventually may need a conference with a 3rd party.

@mjhughes : i like this idea. Students discuss before passing paper & feel a sense of collaboration rather than competition. Competition doesn't provide good atmosphere.