I think your first step is to go to your sons school and do some observing.There are some key things you need to watch for:
Is your son acting the same at school as at home?
If yes,
What does the teacher do?
Does your son respond appropriately to the teacher?
Are other students acting similarly?
Are other students giving your son attention?
Let me just say that if you don't like how the teacher responds to your son, you may as well just switch classrooms right now, cause talking to them will only change what they say, and not what they do. It is generally true that teachers are more responsive when parents are there, so don't expect more when you are not. But if you do like the teacher response, try to copy it at home.
If your son is not acting the same at school:
Still see if other students are acting similarly
Ask the teacher if she noticed behaviors in the past - there is a good chance that your osn, or a different student was copying, and the teacher nipped it in the bud.
It is important for kids to spend time with people of all ages and abilities, and copying certain behaviors will happen all the time, we just complain when they are bad behaviors, but that is how kids learn. If your son is still only picking up negative behaviors, then you need to find a classroom where there are more positive influences.
Even if itmeans finding a private school, you don't want to let these things get out of hand. YOu don't want your kid to be the "bad" kid at school, or the parents that have children who are good influences, might start limiting their time with him. It sounds harsh, but its true.