What a week so far

It has been a rough week with the boys. My twelve year old is having a really hard with school. I dont look forward to nights at home with him and his attitude and homework. It seems its always a fight to get him to do anything. He is in the 6th grade and he is failing and they are already talking about holding him in the 6th grade for another year. I really hate it, I have such a smart boy but he doesnt want to do the work. He just doesnt care about his school work. What brings his grades down is the homework and class work. He gets mostly zero's on all his work, because he just doesnt want to do it and what we do at home he wont turn it in. However when it comes test time he makes 100's + on all tests but they dont count enough toward the over all grade to make the grades high enough not to be f's I cant get him to understand that he cant fail that he needs to try harder and do what he has to do whether he wants to or not. I have grounded him from TV, video games, made him stay in his room, nothing seems to matter. Back at the begining of this grading period he was acting up in class and he had really long hair so I made him shave it off. He was so mad at me for doing it but he was acting like a hoodlum and I didnt want him to look like one as well. We cut it off. I told him if he brought his grades up that he could grow his back out long and he dont care about that anymore. He is fine with it the way that it is. He had detention this morning before school today, because he was throwing pens across the room at another student. Of course he lied about it said the teachers are all against him. That they just dont like him. He thinks that all adults are against him, he tells people that I hit him. I dont hit either one of my boys and I know one day someone is going to hear that and turn me in and then it will be a big mess. I have tried to explain that you cant say those things when they are not true ...because of all the people you would hurt and including yourself. It doesnt matter. What do i do with him...