It's very important to have an answer to the questions that seem to have been raised about your son. First of all, you need to confirm that he has ADHD (the current terminology for attention deficit hyperactivity disorder), and you need to know for sure if he has Tourette syndrome. You haven't said whether or not your son is using medication to help with the attentional problems, or for the Tourette syndrome. Sometimes the medication used to treat ADHD can make Tourettes syndrome worse. Unless you are absolutely confident that the person or persons who made the diagnosis are correct, then I would suggest you take your son to a professional who specializes in the diagnosis of ADHD, such as a pediatric neurologist, a clinical neuropsychologist, or a psychiatrist. Your son's pediatrician can make a referral for you, or you can contact ADD-In (781-455-9895), CHADD, or your state's office of the Learning Disabilities Association of America. Since your son is failing two subjects, the other thing you want to be sure about is whether or not your son also has a learning disability (which is often seen in students with ADHD).
Since your son's problems seem to center around poor organizational skills, I'm wondering whether the folks in the resource room are doing enough for him. Do they have a system that requires him to check in with them before the end of the day to see if he has his assignments written down, or the first thing in the morning to see if he has completed them before going off to class empty-handed? Some high schools say that it is unreasonable to ask teachers to play this role, and that a 16-year-old ought to be taking more responsibility for himself. This response is rather like a teacher saying that a child who is blind ought to figure out how to read print materials -- it doesn't take ADHD and its consequences seriously. While it is true that your son can learn to take more responsibility -- right now, he can't or won't. If he's doing well in other subjects, it could be that he has little motivation for biology or geometry. It's important to find out how your son feels about these two subjects. Does he see them as relevant to his future? Does he believe that no matter how hard he tries, he'll never do well? The trick here is to find out what's getting in his way, and to get him back on the track to success (especially since he apparently has a lot of potential that is not being tapped). If these courses are too much for him to handle at the same time, you might consider having him drop one and take it later. It's better to successfully complete a high school program in five years, than fail it in four.