First I am hoping that the parents are on board with you and strictly enforce punishment when necessary. If not..any action of yours will be undone the minute he leaves.
Also, you may want to speak with his parents..has he been around another child that has this behavior? A DCG of mine is totally not herself after spending a day with her cousins. They are rough and spoiled to say the least and it takes a day or two to get her back to normal. So it is likely he has been spending time with someone with the same demeanor.
If not..like I said before while it is possible he is simply going through a terrible age (I call it terrible threes because with all three of my kids as well as DCK..it has always been age three for the worst not twos!), if his demeanor is not corrected every single time..it will continue beyond those years.
Another question, has he had any changes at home or with you lately? Have you added new children younger than him that require more of your attention? Has his schedule changed? Any of those can cause emotional issues with otherwise well behaved children.
Good luck!!
