I happened upon your post because I keep Focalin as a search term on my Google page and couldn't help but notice some parallels between your son and mine. You've already received some great advice.
What I can add is my personal experience and what has helped our 8 year old son who is currently taking 10mg of Focalin plus 150mg of Welbutrin a day. I'm not making any assumptions on what you might be doing or not doing this is what works for us and we have to stay vigilant with our methods otherwise we see a change in his behavior. So here's what we've done for our son...
I knew my son's behavior was difficult but didn't realize how outside of normal until he first started kindergarten. (He attended preschool for 2 years but his teachers were more willing to work around his behavior so it just wasn't as obvious to me) He was expelled from school at the end of his first month. That was the beginning of our wake-up call that something needed to be done.
Sleep - we discovered he had sleep apnea. So with surgery to remove his tonsils he sleeps much better. He also uses a 6lb. weighted blanket and that helps him sleep more soundly and gives him comfort. He takes 1mg of melatonin every night too since he hasn't been able to go to sleep on his own before midnight since he was 3. I was hoping that the welbutrin would help his sleep patterns because I have a low dopamine level and it's helped me with mine. He's been taking it for a month and I'm not seeing much of a difference.
Discipline - I took a non-violent communication class called, Nurtured Heart, it is for parents with difficult children and I learned some effective methods for my son. Really clear consequences, no warnings for misbehavior. If he does something wrong he gets a consequence (one that has already been established prior to the misbehavior or one that is reasonable) and total follow through. And when he does something right he gets a ton of praise. Not "Good Job!," but "Wow, I saw that you cleared your place without me asking! Thank you so much." and do it all the time, more than a child without ADHD would need. And even for the little things so he hears that praise as often as possible. Especially when he does something I've been asking of him over and over and he finally does it without a reminder. This made a huge difference for our son. We also asked his teacher to use it with him and it made a difference at school too. To us it felt completely over the top but he ate it up. It was like we were filling his ego in the healthiest way. We find now that we don't need to praise as often because he doesn't crave it as much. But he still gets a lot of praise.
A few months ago my son started to scream every time he got in trouble. It was completely ridiculous. I knew that no amount of nagging was going to quell that response so instead I had him make a poster where he had to write at the top, "Instead of screaming when I get angry I will..." and then I let him list all the things he wanted to do instead of scream. Then we taped it to his bedroom door. It was great. No longer was it me telling him to stop but him deciding, "Oh ya, I'm gonna run 3 laps on the drive way." I didn't get angry when he screamed. I would remind him to check his poster and then decide how he was going to handle it. It took a couple of weeks but it worked. And resets. Instead of timeouts when he starts acting up (which they're too old for now in my opinion) we do a reset. Send him to his room to reset. He can come out when he has calmed down or thought about his actions. Sometimes he stays in his room for a few minutes, sometimes he comes right back out but it usually works.
Routine - He has his own chart for getting ready in the morning. One he helped make and that he carries throughout the house while getting ready for school. It's been a great boost to his self esteem and now he gets a little dose of it every morning. I still make his breakfast and lunch but he does everything else. It's been a huge help to me too because I have three sons, his brothers are both younger than him and now I have adequate time to spend with them in the morning. Our evenings are regimented also.
We are open with him - Our son knows he has ADHD and that is why he sees a psychologist every few months and why he takes a pill every morning. We tell him that this is something that he'll have to work on for his whole life but right now we get to help him and as he gets older it will probably get easier.
Support - I found getting him involved in an organized activity outside of school was also helpful. Soccer and baseball were terrible. He is not a team player but loves socializing so we put him in tennis. That was great for about 6 months then he got tired of it. Now I'm trying to get him into cub scouts and I'm thinking about bowling. Having another role model outside of the home is really good.
Diet - We tried an elimination diet. Took everything but I think turkey, rice, pears and carrots out of his diet for 2 weeks. All we figured out was that dairy was causing his eczema so that was good and that red dye really does effect his behavior. He gets totally jumpy and impulsive with any red dye.
Organize - His room is more organized than the rest of my house. He has a place for everything so he's not frustrated with where he put things or can't focus on his homework because his desk is a mess.
My suggestion, if you haven't already tried some of the things I mentioned, give some a shot. My son was expelled because he cut a girl with scissors! Totally freaked me out but he did it out of absent mindedness, impulse and without regard for someone else. Instead of working on that immediate problem we worked on all the other stuff that might have lead him up to the situation.
I think home schooling is a tough situation for a child with ADHD. They do have the potential for more one on one support but it's from their parent most often. I feel that kids with ADHD need a lot of social interaction so they can learn appropriate behaviors with their peers and exercise. PE and recess are so critical to ADHD kids. An IEP might be a good step too (not one we've taken yet but are thinking about) because, from what I understand about an IEP/504 plan, is it helps protect your son from excessive punishment, you can say in his plan that it's unacceptable him to be taken out of class for half a day. And it provides you with additional services.
I know I wrote a lot but it was a long journey to get where we are now with our son. Remembering the desperation I felt for my boy to be at ease and in control. I feared that maybe he had oppositional defiance disorder too but I don't have that concern anymore. He still does stuff where I'm baffled but it's far less often and I have to remind myself that he is an 8 year old boy after all.