Unfortunately I don't have many words of wisdom, but I can relate with DS4. He started a Montessori school in January and has done wonderful, no problems at all...until 2 weeks ago. It is odd because he does well most of the time, but he just does random unacceptable behaviors sometime. When asked why, he says "I don't know, I just felt like doing it" It is very unlike him and we are shocked. I do know that the school has told me they are unable to challenge him in math because he is above everything they have there...and he loves math. There are still some other challenging things there but I think he sometimes needs more mental stimulus. I don't know, but I have bunches of theories with my DS (of course this is kind of part of my job as I do behavior plans with kids and figure out motivations behind behaviors). I think it is telling that it happens with your DS during K. What activities does it happen during? Are they academic, or social based activities? Is it more unstructured time? I know with my DS it is often more unstructured time and he is not always sure what to do with himself. I fear that things could progress to aggression when our DS starts school next year, he is skipping K and going to first...but still I think if they don't do lots more acceleration he will get bored and act out. I am hopeful that it doesn't happen...but it's hard to say.
You may have already done this, but I would also give him replacement behaviors that he can do instead when he is angry. Talk about other possible options and practice them through role play. It's also good to practice the whole "stop, relax, and think" routine, to help children make better choices when they are upset about things or about do make a poor decision.
