[kisito]

Yes Denis is right that teaching the wrong grammar rules makes things worse for the next teacher. In the same line of thought I wonder if you have the same experience of meeting many ESL teachers who do not even know some basic grammar rules. Well sometimes we can't avoid teaching rules because students ask for them. I can't begin to count the number of times my Chinese students ask for a grammar rule. This makes teaching of grammar rules inescapeable. But I have met many teachers who do not know basic grammar rules, and so cannot explain them. It may seem ok because they learnt using a direct method and were born in English speaking environments. But as a teacher, you will always get students asking you why we use a particular grammar form. Even with the rules, you cannot explain everything. So I always try to make my students see grammar as one expert did. She said that grammar rules are like the scaffoldings on a building, necessary at construction, but unnecessary after.
I should go on to say that teachers need to perfect their grammar knowledge and explore better ways and exercises for teaching, practising and reinforcing then, when and where necessary. Grammar rules, as imperfect as they can be, define a language and are therefore a good base to fall back to.