Steven Biddulph in the book, Raising Boys, recommends starting boys a year later in school because they are not ready for a rigorous academic environment that requires them to sit still. So maybe it's just asking too much of him to have him sit still all day. Maybe he can wait another year before starting school? Or have you considered putting him in Montessori? I know of a charter elementary school (meaning it's free to send him there) on Recker and Elliot called San Tan Montessori. They also have preschool (but the preschool costs money) there if you want to send your younger child there.
I would also like to agree with the person who recommended Love and Logic. Here are the list of classes the local Love and Logic instructor is teaching: http://www.keriparentcoach.com/447486.html Tell her T. sent you. You can also call the Love and Logic company at 800-588-5644 to get the contact info for people who teach classes in your area (I just called and a real person answered right away and was very helpful).
The Love and Logic approach is all about tough love--being firm and consistent in letting children suffer the natural (logical) consequences of their actions, while doing so in a very gentle and loving way, having true empathy in your heart.It sounds like maybe you could ease up on trying to control his behavior and just let him suffer the natural consequences, or maybe more empathy on your part is needed. Try to see where he is coming from and remember being a child or even being an adult and being denied what you want. It doesn't mean bad behavior is acceptable, but feeling frustrated is. My mom parented this way, and I really appreciate my upbringing. I feel she was a very effective and loving parent who helped prepare us for the real world.
If classes aren't available near you, check out some Love and Logic materials at the local library for free or buy them at www.loveandlogic.com. Here are some I recommend: a seminar on DVD "Painless Parenting for the Preschool Years," the book "Parenting with Love and Logic." They also have some great CDs full of wonderful advice and real-life applications that you can listen to in the car while driving.