I know that child! See a Developmental Pediatricrian as soon as possible for a full evaluation. If you have not had a comprehensive evaluation, then you cannot say if it is ADHD or not, and my guess is not, but you should let a professional decide based on hours of time spent and pages of evaluation data. This boy deserves to be treated with a comprehensive plan that takes into account all that is going on here, and I don't think that you are there with a medication trial. Medicatiion is a tool, a very good tool, but it is used to help children with focus issues to get the most out of the therapy and interventions they need to be more typical. Your child needs these.
You have already discovered that nothing you are going to do that works with typical kids is going to work with him. That is the time that you need to find out how his brain functions so that you can help him. When a child has the intellegence to understand everything you teach him, and then lacks the ablity to apply them to himself nor the abilty to supress any impulse based on his knowlege, than THAT is the process you need to measure and have therapy to help. That very process of inhabition and application/generalization of whta they know is the basic issue that makes typical dicipline imposible for kids with developmental issues, and you are not going to get the kind of targeted intervention he needs to progress passed the point he is right now with out it. Call the nearest Childrens Hospital and make an appointment for a full developmental evaluation based on the behavior you see, and do not ask for an ADHD evaluation, because that is not what you want at all. You want to know what is going on here, and if it is ADHD, the evaluator will tell you that, just as if it is something else, they will tell you that.
The Developmental Peidatrician will be asking you questions about his prenatal, birth, and new born experience, so if you have contact with his mother, you need to ask her some really tough questions so that you know the answeres, and the questions are going to be about her alcohol and drug use, as well as prenatal care, his apgar scores, his new born ablities, and so on. It iwll do no one any good if she lies about drinking during her preganacy, if there is any way that you can get honest answers, do it.
At 7, with these issues, he cannot be doing too well in school either, or I would be willing to bet that his behavior is about to overwhelm his learning experience. Go to www.wrightslaw.com and learn about advocating for educational needs. Behavior is an educational need when it interferes with the learning process. Read a book called "All kinds of Minds" by Dr. Mel Levine.
You may have to wait for quite a while for the appointment that you need, so find a board certified child psychiatrist and see them, and use this professional for treatment once you get the full evaluation. Ask them for a referal to Cognative Behavioral therapy and get started with that. It is possible to start some thearpy based on what you see without a diagnosis, but don't skip the comprehensive evalaution, because I think you are missing a great deal here that you can get intervention for.
M.