It sounds like a tough situation for all three of you -- you, your son, and the teacher. It also sounds like a response to stress in your son.
You and the teacher should talk in person to come up with a plan, and how to implement it consistently. The two of you working as a team can make a lot of difference.
There should be consequences for his behavior, but it should not be seen as punishment. He may already be worried that he is a bad boy, and he needs to focus on the positive rather than feel worse and worse about himself.
When he hits or does things that are inappropriate, he should be removed from the situation, and it should be called "taking a break." You and the teacher should tell him, "I'm not mad. I know you made a mistake. But you can't be around the other children until you're ready to be safe. We have to make sure that everyone is safe. When you feel calmer we'll figure out how to make things right, and you can rejoin the class after [apologizing/cleaning up/etc.]"
It's important that neither you nor the teacher raises your voice or sounds angry. You both need to be totally calm -- easier said than done, I know. But if he knows you're angry, he'll feel scared, and even more stressed out. If you both stay calm, he'll know he can trust you, and he'll slowly but surely become calmer himself.
Sticker charts may help; it's worth a try. He can earn stickers for doing each part of the day (lining up, recess, morning meeting, bathroom, etc.) without problems. He can then bring the chart home to you, and if he has enough stickers, earn a special treat like extra tv or a snack or whatever you think will work.
Good luck! And remember, this is not unusual behavior.