It really does take many, many years to hone written narration skills, so just try to keep encouraging him.

I think I would just give him the sentence starter for a bit - that is what HOD did in earlier guides anyway - and it may be he just needs some time to get back into the swing of school. I know my dc don't write much all summer, so getting back into the writing of daily school takes some time.

I'd just give him the starter, and tell him that there is not one right way to do a written narration. So, you coaching him to write the sentences you are thinking of would just be him writing your narration, which is not the goal. It really helps me to review the Written Narration Tips in the Appendix with my ds at the start of the year. That helps put in place the thought that there is not one "right" narration, but rather all narrations are different from one another to reflect each person's own individual thoughts on what was read.

There are some good tips in the Appendix for helping dc along with written narrations, but I think going over the tips, giving him a sentence to start with, and accepting what he gives you as good enough will help ds ease back into them.

HTH!
In Christ,
Julie