A few observations:

The language teacher in us seems to be answering this question with an ideal student who comes in at level zero and progresses through all the skills. Shift that model to a student who is fluent in a language and must learn to become literate in that spoken language.

I have met many such cases in the Gulf. (Yes, the one located between Iran and Saudi.) I would say the objective then is to have the structure laid bare so that one can understand and expand upon the existing vocabulary and chunks of language which one uses to communicate with others on a daily basis.

The question then becomes "Has one learned a language if one can communicate fluently with others?" Native speakers themselves must be instructed to pass into the literate stage. One can sound out and catch the meaning of a known language. For example, a student who is totally fluent in spoken English of the Southern United States might be taught to read and then could probably understand a dialogue from Mark Twain.  

Grammar instruction is probably advisable for most second learners if the student is not actually fully fluent in the language. Also, if the grammar is significantly different than the first language, those differences should be highlighted. We can extend these conclusions to first language learners who are speaking a “dialect of their native language” which has alternate grammar structures.

I have come to these conclusions from my own personal experience with the Arabic language.