dealing with excessive absences?(Long)

To answer the questions about my original post, his mom and dad were divorced over 10 yrs ago, and she remarried within a year after so I don't think it's to do with a divorce. He has always had attendance problems even in his old school. When he first started at this school, he said he liked it now he won't go, won't do homework or study and is failing and he says he doesn't care. He does have a couple of friends he talks about so I don't think it's loneliness at school. His mom isn't home during the day she's a DON at a nursing home so she's working while he's supposed to be at school. I don't think it's to keep her company. She never really had him anyway, he's basically lived with his grandmother since he was a baby, but she never let his dad have him. He has a problem with his temper, he doesn't follow rules like bedtime, cleaning his room, doing homework,etc. He punches walls, throws things, etc.. He gets mad when we try to make him follow rules and do things a normal 12yo should do. He thinks any form of discipline is child abuse and says we will go to jail if we spank him. He's ridiculous in the fact that he thinks rules don't apply to him. One of his teachers got on to him at school and the child thinks the teacher should apologize to him! The mom blames the school and they've bent over backwards trying to help him. She never goes to meetings with the school, his dad does. I don't know what to do with him, he thinks everyone should kiss his a@@ and he's 12! The problem with his temper is I'm afraid he is going to hurt my baby. It's due in July and he's got such a temper, I'm afraid he'll do something. He threw a remote at my mother in law and once tried to intimidate me with a kitchen knife. I'm lost and totally stressed, any advice would be greatly appreciated!