He sure sounds ADD or ADHD to me, and I've both been there and didn't want to medicate, either, and am there and do medicate to some degree. I have three suggestions.
1) To start off with, check his diet. Get him onto as much organic, additive and preservative-free type food as possible. This helps some. Start giving him a good Omega-3 supplement, too. (Check out New Vision and, if you can afford it, get their liquid trace minerals. They help a bunch.) Some ADD kids do well with some caffiene, too, like Coke or Diet Coke.
2) Then, do your homework. Read as much as you can. Once you understand that he is trying to process ALL of the information around him and can't sort it out, you are on your way to understanding. Go to websites, and bring your husband along on your journey. You both have to be on board if you end up needing to medicate to some degree. When he sees that the boy fits the profile and understands that it is his (dad's) responsibility to help him deal with it, see if you can take your son to a psychologist that specializes in ADHD. Some insurance actually has a mental health provision and it will be covered under that. Consult your pediatrician if the psychologist says it is ADD/ADHD. We use Adderal Extended Release; it works better for us and covers most of the school day. Adderal does not build up in the blood stream, by the way, which is why the pediatrician prescribed it. It is in and out. She started out on a low dose and built to the point that works best for her. At 16, she takes it only on test mornings or days that will have a lot of distractions for her. She doesn't take it everyday, though some do.
3) The rest involves getting your son to take responsibility for the parts he can: homework and assignments. Make lists of what he has to do each day. We had an arrangement with the teachers (work with school specialist on this) to have them sign off that he has written down the assignment and has turned assignments in. Keep in touch with the teachers. He needs to get into his head that the FIRST thing he does for each class is to hand in homework. Can't get credit for what the teacher never sees. Then, make an appointment to meet with his teachers and have them help hold him accountable. The test/quiz thing is a hard one, and a common problem. It is a problem for us as well. He probably freezes and does not do well on timed tests. Talk to his teachers; get him more time, and see if they can figure out how to test him differently (some will do it orally, which works for us) or non-test him, which means he gets special assignments which take the place of tests. He will have to learn to do standardized testing, though. She now deals pretty well with everything but math tests. Oh, well.
I wish you well on your journey. Your son is probably very bright and creative. Most entrepeneurs are ADD. He will have to work hard and take responsibility, but with a little help and perseverance, he can do wonderful things.