I taught
ESL for 17 years, John. All of that time was spent in Japan. I taught students from 6 to 60, university students and research scientists.
I'm not completely sure just what this particular functional approach entails. I know that "functional" is the only way to teach languages. It's done all the time with every child in every language in the world and children seem to do alright. It's only adults and adults who "teach" that produce non-functional/non-functioning students.
Could you expand on the approach of that American grammar book, please?