I have an 8th grader with ADHD who's been like this since 4th grade and I've taught junior high in the past, so I understand both the frustrated parent and the teacher perspectives. You have already received a lot of good feedback. I would like to emphasize the following:
1) This too shall pass. Your son will ultimately be fine. I know this because you took the time to pursue his teachers and to seek out help from this online community. For most students, the most important determinant of their success in school is the degree of parental involvement (there are a multitude of studies that show this).
2) Continue to monitor your son. I use a daily report form that I created for my son because the school's form did not meet our needs. It has a line for each teacher with four questions - did he treat you with respect? did he treat his peers with respect? was he on task? did he turn in his homework? The teachers rank him on a scale of 1-5 for each question and then sign their initials. Then there is a space for them to write comments if they so desire. I sign under their initials each night so they know I read it (this sends the message that I am willing to invest the same extra time that I am asking them to invest and that their time is not wasted because I do look at the form every night). The important thing is to keep the form as simple as possible so the teachers can easily fill it out in 30 seconds near the end of each period. However, tell your son to give it to them at the start of class so they can make notes and do it at their convenience.
3) Link consequences to his actions (positive and negative). For example, if my son earns a 1 or 2 on his report, I take away privileges (t.v., computer, etc.). If he doesn't get his homework done, he has to catch up on his work instead of getting to go to track practice, for example. If he earns a 5 I reward him (praise for one day, ice cream at Cold Stones for all week, etc). Let your son help determine the consequences - you will get more of a sense of what motivates him and more "buy in" from him. Notice there is no consequence from me for 3 or 4, this is because I expect this level of behavior from him (small errors, not perfection) and his consequences are thus simply the good grades and relationships with teachers and peers that naturally come from this.
4) I've found "I'm bored" means one of three things:
First, it can mean "I'm tired and don't feel like getting started" (procrastination). Second, it can mean "I don't understand this work and don't feel like trying to figure it out." And third, it can mean "I don't find this subject very interesting and don't feel like doing it." You need to teach your son how to identify which "I'm bored" he's feeling in each situation, and strategies for overcoming it. For example, the only way to overcome procrastination is to "just do it!" that's right, exploit popular culture like Nike if you have to. I find that if I help my son get started on an assignment, once he gets going, he will usually finish up on his own without needing much pushing. A popular strategy used by teachers is to get kids started on homework at the end of the period for just this reason. If he consistently doesn't understand the work (the second "I'm bored") then he's either missed a foundational step and needs remediation or he lacks study skills. In either case, he needs tutoring, either after school with the teacher or at home with you or a hired person or center. Make sure the tutoring focuses on the actual root cause of the problem: missing foundational knowledge or study skills; and does not focus on the content he is learning in school right now. Finally, the third "I'm bored" (lack of interest in the subject) requires a very important realization on your son's part - he's not always going to like or be interested in the things he has to do, but he's still got to do them; and no one wants to hear him whine about it. Once he understands this, you can teach him strategies for how to make boring things more interesting. The best way to do this is by finding something about the subject that's relevant to him. For example, my son thought cell biology in 7th grade was so boring until I started showing him websites about cancer and pheromones. Unfortunately, only the very best teachers are skilled enough to make their subjects and assignments interesting to all students - so you're going to have to step in and pick up a little of the slack here. Another strategy is to make a game out of the work. When my son was younger and the math was more straight-forward practice, for example, I used to divide his assignments into equal segments and then time him on each segment to see if he could beat his previous record. Eventually, he started developing his own self-motivation (with a little guidance) and now sets small goals form himself like, "I'm going to get a snack when I finish my first assignment. I'm going to play a round of Mario Brothers when I finish my second assignment."
5) Finally (I promise) realize that his hormones are making him very moody and while these strategies may work well sometimes, other times he will be totally beyond reason. When this happens, give him space. When he's "rational" again, get things back on track. Sometimes when my son gets into the car after school and I ask "how was your day?" I get screamed at. I've tried all kinds of different responses to this and have found the best reaction is to just keep silent in the car; then when we get home, I tell him, "I do not appreciate the way you just talked to me; I'd like you to go rest in your room until you feel more in control of your emotions." If he argues, I calmly repeat myself, until he does as I ask. Often he falls asleep for an hour or so (children, even teenagers, need 10 hours of sleep per night - especially athletes - and often don't get it.) After his rest, he is usually more reasonable and receptive to me and to getting his homework and chores done. He even apologizes on occasion for screaming at me and will hug me and say, "I love you Mom." Now that's something to be grateful for!
Good luck C.; and I sincerely hope these comments help!