Just a small point, but there's a lot more to a language than the grammar. The finer points of grammar are interesting, but one danger I have seen countless times is grammar being used as a crutch or almost as a weapon against students in some systems, where students are bombarded with terminology and the main aim appears to be to make the teacher look clever rather than to teach anything.
(BTW, I should point out that I am talking in general here and not about anyone in this thread, but we do have endless cases in the forum of beginner or low intermediate students who can barely string a simple sentence together with a task such as distinguishing between present participles and gerunds, an activity of interest to grammar buffs, but more likely to confuse and put off learners at lower levels.)