When our English teacher in our English language high school in Geneva decided we should do some grammar he quickly realized we didn't even have the basics. He solved that problem by switching to French grammar to explain the English version since most of us had a good grounding in that - so a native English speaker explaining English grammar in French to a majority native level English speaking class.  But I only really learned some grammar when I taught ESL in Poland after college - I realized I had to teach myself when on the first day one of the kids asked me something about phrasal verbs - something I'd never heard of before. And as for Polish grammar all I know I learned in Russian classes in college and grad school.