My seven year old son does the same thing!!!!
What I do is send him to his room when he starts acting out. He pulled the tantrum thing on me once this summer. First I sent him to his room (with the door open) so that he could calm down, and I told him to come and get me when he is ready to talk about it. Every time he would come out, I would look at him straight in the face, and ask, "Are you ready to talk to me so that I can help you?", if not I would ask him to go back to his room and think about it, and when he is ready to come and talk to me.
The trick is though, you need to talk to him/her when they are ready, and not in the ignoring stage or "clamming up". So, if he walked out of the room and did not answer me, he would have to go back to his room. I tried to set the timer for how long he would have to stay in his room, but sometimes he was still not ready to talk, or he was ready to talk, but the timer had not gone off. That and he would yell "no, not the timer!" over and over again every time I set it, so it seems to work best when I allow him to come out when he is ready to talk. That and usually by the time he gets into his room, he is quiet, which is a lot better than him yelling about how much he hates the timer.
When he was done thinking about it, or calming down, we had a discussion about how that is not the way to act. We talked about talking to people that we trust (Example: family and close friends) instead of throwing a fit. I also told him why it is important to talk to people when there is a problem so that we can figure out what to do about it, instead of getting overly emotional and causing more distress to everyone.
Now, when my son gets upset, he gets real quiet, and says, "I need to go to my room and think for a minute", and when he is ready, he comes and talks to me or whoever is there with him.
But now I got to figure out how to help him deal with this at school because at school, he cannot go to his room to think about things and calm down. For that, I have been working on meditation, and "yoga breathing". But he did that once in class, and got into trouble for not "looking" at the teacher, and making "breathing sounds". ugh.....
Well, good luck!
M. *~