My kids walk in the door & go straight to the table most days. They'll have a snack & drink first, but thats it. Homework is first on the list for the afternoon.
Its routine & DD1 (10) is doing ok. She hates getting in trouble at school, so always makes sure its done. DD2 (7, ADHD also) is a nightmare. We're half way through the year & after 6 months of homework 4 days a week, she'll still try insist she has none.
We're getting there

Would your DS's teacher allow him to stay after school to do the homework. I did that for a bit in about year 5 when I was struggling. They do more for teachers then they do for us at home...