How about high school English teachers who decided that they were bored by English grammar (back when they knew it)? Now a kid has to learn English grammar elsewhere. Sometimes the only option a family can afford is to leverage foreign language lessons in school (checking the rep of the teachers to ensure that they are careful to teach grammar). My niece is learning English grammar in her Latin class.
The days are long gone when we all diagramed sentences in fourth grade. Our high school graduates are grammar free, and it will show throughout their careers. Lazy teachers and students can't fake correct writing.
I've done this myself. Not Latin, but other languages.
There's a series of grammar books, "English Grammar for the Student of [insert language here]", for people who need to learn formal English grammar before they can learn other grammars.