Please help! Any advice welcomed!

Let me sum this up with as few words as possible. Jacob has had problems in the past with getting angry and also hitting, like many other children, I'm sure. There has been time in between where he hasn't had a problem but it's come back. We've tried different tactics, the most recent being that game days (days where he is aloud to play video games when I say it's okay) are not a given anymore, he has to earn them. We have a sticker chart for good things he can do throughout the day (like no time outs and brushing teeth) and if he gets them all the following day is a game day.

Today during the last half hour of preschool he was very naughty apparently! I had to stay until all the other kids and parents left to talk with the teachers. They played a game where whoever wrote their name the most times won a prize! I'm guessing they had a time limit. Jacob did very good, they said, but he didn't win and he got very angry. When a teacher attempted to calm him down he elbowed her!! (A new behavior.) He hit the other teacher and a kid sitting next to him on the arm and threw some laminated cards on the floor. His name was getting moved up this whole time. He then looked right at his teacher Miss Heidi, and as he watched her watching him, he dumped a can of pens out onto the floor. Miss Heidi asked him to clean up the stuff he threw on the floor and he said, "No." She told him that his Mommy doesn't like it when he acts like this (or something like that) and he said , "I don't care. It's not a game day today anyway." (He was quite disobedient yesterday and ended up getting a time out). He had to sit in a chair away from the others for the rest of class (about 10minutes) and even continued to try to do naughty things to get their attention while sitting there!

His behavior has never been this bad! Oh, he was kicking too. And he's never carried on like that either! I realize that I wasn't there to firmly put my foot down and that there is only so much the teachers are allowed to do, but still! What's going on and how can we help him to keep control of himself when he's angry? He has such a temper.

Oh, I should mention that he is very dramatic. For instance, if he goes to see if the kids across the street can play and they either can't or they're not home he howls and cries about how, "Now I'm never gonna get to play with them!" I also wonder if he has low self esteem. He says that he likes himself and that he knows that his classmates like him though, so, I just don't know anymore. What do I do?? Is this a normal phase or is there something more going on??