What to do when the student disrupts the class? It would be better if the student would not be confronted and that the teachers try to get at the emotional reasons behind the disturbing. This is because in order to get to the root of the disturbing behaviour one has to allow the student to express himself and have him accept that his methods are counterproductive. It is now many years since teachers were protected from child disrespect as they once were. Even students coming from cultures where teachers are still respected the fact they live in North America has exposed them to the "pollution" of the peers in being unresponsive, rowdy or disrespectful in class.
Parents will need to know if disruptive behaviour continues, different schools apply different approaches. Some Asian schools will tell the student out rightly that their parents will be advised and most often a fear factor works to keep the children in-line, however that statement should not be abused.
Good students need to know that they are helpful in assisting how they contribute to the class flow. Often the teacher should take advantage of their presence especially if there is a mixed class and some of the students are behind the others. Then the poorer student will have a model to follow from a peer instead of from an adult. Sometimes the poorer student can be paired with the stronger one so that he can catch up and copy some skills unconsciously.
The student who is purposely disruptive should be spoken to but not accused as that would only cause discomfort and promote isolation between him and other students. He could be coaxed into talking about why he is disruptive or rather how he intends to learn if his interruptive behaviour gets in the way. Naturally one assumes that the child wants to learn otherwise one has to be persuasive enough without threatening him. I am not one to think that raising your voice is going to cause havoc to the child's brain but I would use that at a last resort especially if conditions deteriorate. In the end smaller groups are easier to manage than larger ones if the teacher has a choice and getting the problem kid to be more a participant instead of excluding or reprimanding him would be better. Positive reaction towards negative behaviour might get a positive response.