One of my sons also has ADHD (hyperactivity and attention combined). I know how hard it is to get him to sit still. With this son it takes extra patience and more reminders than my other son.
From my experiences with my son some things I learned are:
1. Keep my lessons short (1 video lesson 1 story) unless he asks for more
2. I use points per story read (3 points=perfect effort, 2 points good effort, 1 poor effort) 20 points equals a toy worth about a dollar
3. I make a reading routine (eat, shower, read, TV/ Ipad)
4. He needs to point to the words as we read
5. Sometimes he sits on my lap/or next to me and we point together
6, Some time he sits in a chair
6. He reads and watches the videos wiht me but not with his brother. He needs no distractions
7. We do not read every time. Some days we use the Flashcards. He feels the Flashcards are a game and he likes to play more than sitting and reading
8. I tell him that reading and learning is his job and his points are like his money he makes from hsi job.
Hope this helps!