Why so many students who have learned English for years are still poor in English
It takes so many students so long because the students cannot understand how English Grammar works.
The students cannot understand how English Grammar works because their teachers cannot explain it to them.
The teachers cannot explain how English Grammar works to their students for the simple reason that they do not know it, either.
The reason for this is even more simple — it is impossible for anyone to understand how English Grammar works using the term Tenses. https://medium.com/@LHmury/the-biggest-pain-with-understanding-english-grammar-3476aff6bfee#.5kqfnjlxf
With Tenses, there is no way to see, and therefore explain, either what the REAL Verb System in English Grammar is, or its logic, or how it works.
This is why the process of learning the language can be seen as one hundred per cent (100%) memorizing without understanding and looks like a gradual growth or a gradual transition from one proportion to another, i.e. a slow transition from quantity to quality. No wonder it takes years.
Alternatively, using the logic of Natural English Grammar, THREE MONTHS is more than enough for any English learning student to understand the way English Grammar works (= the logic of constructing and understanding English sentences).
After that, it is memorizing WITH understanding.
Feel the difference, as they say.