N.,
Does your 6 yr old have a learning disability, giftedness or something that would cause frustration at school?
For example, my son is "gifted" as the school testing put it. For years we had some social/behavioral issues....nothing MAJOR but enough to cause concern. He had trouble cooperating with simple things and would fight authority... Upon reaserch I found this is NORMAL for very bright students.
He was getting in trouble in 1st grade last year because he was bored. Talking, acting like a clown, etc... which is also a normal behavior. It helped up to be told he was "gifted" because it has helped us seek alternative discipline and helps us understand him better.
It seems that both ends of the spectrum have issues being addressed at school. So this may or may not be a source of frustration.
Or maybe there is another kid bothering him, that is causing him problems and his lack of experience tells him to act out this way.
I hope this at least gets you thinking outside the box. Don't let anyone tell you he is a bad kid or a problem. This is a behavior...NOT your kid.
Blessings.
M.