I would say that Jennifer's response (in the other version of the question) was probably most accurate. Your answer pool is automatically biased towards more formal grammar education due to the fact that the question is posted on italki, a site dedicated to language study which will naturally have a group of more language aware users. It's probably less true in more bilingual areas such as England, maybe Australia, but in the US (the midwest in particular, as that's where I'm from) most people know grammar rules naturally. They're actual knowledge of that grammar is quite questionable. If you asked them where the adjective was in "The red bus drove down the street quickly." they may or may not be able to point it out. If you ask them when to use I and when to use me, they probably wouldn't be able to give you an accurate answer. The language is a natural flow for them and they don't know the real rules, they just know how to obey them.

English in school was a pain. Diagramming sentences, identifying dangling participles and adverbs and adjectives and remembering 'i before e except after c' for spelling. I suppose it all paid off. Good grammar comes from good schooling and good practice.

Hello Alex, Since it is their mother tongue ,they learn at early childhood speaking almost correct English at home. At school they learn grammar through grammar books. The grammatical rules are explained and practiced through exercises.

just like we learn our grammer rules,actually,just remember the basic rules and learn how to speak and write . The more you write and speak the more grammer you yill learn.