Not always well. One of the problems is that English speakers do not get taught the proper parts of speech. I learnt far more about English from learning other languages than I ever did in English class. We would get told off for bad spelling and grammar, but very little on the actual mechanics.

English classes (at least at my high school) were largely about literature, less the language itself. Though I did take one elective class on grammar.

Yes.

All through middle and high school, so for 7 years from around 10 to 16. It did become one eventually in primary school, so probably the last 2 or 3 years there.