It may be a good idea to look into why he is doing this ,is he the only one , are there no other children hitting, could he have learned this behavior from anyone , you say he wants to saty with the teacher in school this sounds like a child who has been bullied , look beyond the box..ask him questions about others and hitting ...it may not be all about him .Good Luck
is this a new behaviour? I would look into getting professional help.
Perhaps you should take him to see the doctor, and a child psychologist. He has some problems that seem to big for you to handle without some help. He is clearly angry at someone, or something and perhaps something has occured that you are not aware of that has triggered this behaivour. Was he always angry or is this something that has started recently.
good luck to you and your son.