I am teaching a gentleman who has lived in the U.S. for over 15 years, but has problems remembering to say and write the "s" when speaking. For example:
The group leader of the meeting all met to talk about progress.
Our meeting are every week at 3:00 pm
What kinds of exercises can I do to help him?
I'd suggest drills. Parts of sentences given only. 15-30 of there for each person, and you might end up with an imprint in his mind. :)