i know how you feel, my ds(4) has been realy naughty for just over a year now, been trying different things, but either nothing works, or it works for a week max, his favorite thing is telling me he will cut my head off when he started 4yo kinder this year, i asked his teacher to keep an eye on him and let me know if there is any problems, he was going fine till 2 months ago, slowly started getting worse, the last 2 chats i had with his teacher included him turning himself into an animal, hiding his shoes and snarling at the kids, and snipping sissors at another child, they were trying time out with him, it dosent work for them, as much as it dosent work for me!
his little brother acts like him, but when he is at kinder, my younger son is compleatly different, little angel! just my eldest is naughty no matter were he is, i have seen a peadiatrician with him, she said there is no major concern for his behavior (HA! its not her house he is terrorising!) she sugessted that i keep trying to find diffrent routines ect till i get one that works... and that i should take comfort in the fact he isnt suffering a dissorder or anything making him this way!
the only thig that i can think of is that he could be acting like his 14 and 16 yo uncles (one is a smart a** the othe thinks he is gangster) and my 11yo spoilt brat of a sister, so trying to eliminate sleep overs at grandparents houses, hoping we get results from that....
hope the problems you have with your son works out, there couldnt be a family member/neighbour ect that he could be trying to copy? its so hard when there are no answers, they should be born with instructions for the difficult parts!