What are the grammatical flaws that English teachers usually fall in?

They , most of the time, depend on the written skill rather than spoken skill and also they sometimes use Arabic language when it is not needed.

don't all teachers have the same flaws

i m not english teacher .but i teach mathematics 

they teach not for students but for money.

so first keep in mind that , attract their studens nature and knowledge within that we teach whatevr the topic.

It is not usual. Different teachers have various flaws

The flaws are mostly in the "future tense", the usage of "will", "going to", "verb to be+ing". Also, it can be a disaster when it comes o "while" and "when".

I think that a teacher must be a book and a chalk, how can a teacher join a class without preparing his lesson and read the grammar although he already knows it before but everytime we read we get something new.

As I said a teacher must be a book ,he knows well and keeps the grammar well, during preparing the lesson a teacher should imagine a discussion with his students or he is asked or questioned then he expects and gets the answers, there are also a lot of exercises on every grammar item , a teacher should test himself and answer the available questions a lot of them as he can.

A chalk he delivers what he has in his mind to his student and make it easier and in different sentences which make it well understood and no confusion.

Finally if a teachers prepares well ,and reads well ,he will never fall in that flaws.

Thanks a lot. 

From wat I totlay beleive:

Teaching the grammar out side a context.

Teaching without enough application.

Teaching tha grammar as a grammar.

Selecting iregulares in non suitable education situations.

THE INTEGRATED COMMUNICATION IS A MUST.

THANKS