I found that learning a language without explicit grammar instruction works very well (for me at least, and a few other people I know). The people that I have seen being taught in this way seem to become fluent much faster than people taught with other methods.
I have tried doing research on the topic but I am not a linguist and I do not understand the terminology that the research papers use, and some of it is very confusing. Also, I am a learner, not a teacher.
All I want to know is how does teaching a language to adults, without explicit grammar instruction, compare to other teaching methods?