Have you tried a shorter passage with just him? My kids all narrate better 1 on 1 with no one else there to distract them or give uncalled for pointers. (We’re working on this one) Do this for “writing” or “English” time.
You can also stop after a paragraph and ask for just a 1 sentence summary. You could then even write his sentence for him. Then go to the next paragraph. If you write them all down, then you could edit them into a written narration with him.
I sometimes use promos like what happened 1st then what, then what, to help the children.
At his age, you could also ask him to compare a character to another one he has read about or tell how he could apply a lesson to today. There are some free narration bookmarks on their site somewhere that I find helpful instead of always asking what happened? There are also narration note cards you can buy for some of the SCM suggested spine books that give you other ideas.
The free bookmarks
https://simplycharlottemason.com/store/narration-bookmarks/