C.,
My seven-year-old doesn't have ADHD, but he is a very animated active boy who sometimes has a hard time, as you put it, "staying on task." His teachers love him, because he's really sweet, and gets super grades, though sometimes he just seems to fly over things when distracted.
We have karate lessons available at our school, as a low-cost after school activity. When he wanted to join, I mentioned disipline, which scared him a bit, but he ended up enjoying it. I think the disipline became a challenge he enjoyed. He's since gotten involved with soccer, which is now his passion, but I feel the karate taught him well.
A fabulous book called "Dreamers, Discoverers and Dynamos" was given to me by my sister, and it's great, even if your not one to want to read a book cover to cover. Talks about The Edison Complex, and how Thomas Edison, as well as many other great thinkers, before we had the term ADHD, was called a "divergent thinker." I am a divergent thinker, and I love it! It keeps me motivated, productive and creative!
Best wishes!
H.