The reason I ask all these questions is that all these factors matter. If he loves sports and focuses during sports, he should continue to do them. ANYTHING that teaches an inattentive kid to focus (not counting hours of video games) will help them in the long run.
Melt downs over homework are really common. Forging a plan as a team (it sounds as though you are doing this) helps. Breaking down the tasks into pieces and interjecting fun activities, snacks, breaks all help. If you can meet with the teacher and have her make sure he stays on task at school, this would help. Sometimes asking the teacher for a recommendation of a kid who could do the homework with him (not for him but with him) with you out of the picture helps inattentive kids focus as they tend to "sync" better with someone their own age (Or slightly older. In the 4th grade my son had a neighbor in 7th grade who I paid $7 an hour to be a "homework" helper. Later, I got him a High School senior to be a homework helper for $10 an hour-my son never melted down with the homework helpers and they are cheap!!).
If he likes school, that is a real plus. I do not know what you do but if you could help out at school, that often makes kids feel more like school is a family event rather than somewhere they are "sent off to". Since you had ADD as a kid, try to draw on your own experiences of what helped you. Kids with ADD/ADHD (as I am sure you know) often have other medical/emotional/psych things going on. They all do better if these things are treated.
Let me know if any questions that you might have.