Just a further note on re-reading about your child, and suspected AdHD.
Hvae you spoken to the teacher about the actual work being given?
There could be a number of reasons.
Either the work is not challenging enough, or the level of communication to the child is not plain/simple enough. Either way, i have encountered children in my professional career - they simply get bored either way, and seek attention from others with what may be seen as inappropriate behaviour.....I dont believe there is such a thing as a 'naturally bad' child. After all, racists, thieves,rude, arrogant people aernt born..they are taught it in some way, some place....with possible key factors as a trigger. Get a professional to talk to you AND your child to ascertain the level of work...you may be pleasantly suprised!..Good Luck!