I think it's a given that EFL teachers, once they have gained enough experience, will come to the realization that the pace of their classroom English will differ considerably from what their students will hear when talking to a native speaker. Teachers also learn to adjust their speech patterns in accordance with the level of their learners. Moreover, in the process of teacher modeling, they will present the language in stages until the "true" pace is modeled. During the course of all communicative language lessons, the experienced teacher will also introduce the reduced speech patterns that align with the target language.

I have encountered many ESL/EFL students over the years who have unfortunately been introduced to such speech as "wanna" and "gonna" without getting a thorough explanation. Way too often I've seen students use wanna in their attempts to mimic native speech. In my opinion, it sounds ridiculous. Furthermore, it sounds uneducated - almost as if the speaker has not learned the language correctly. It isn't always necessary to use reduced speech just because you've learned it. What's worse is that when reduced speech is not properly taught it enters the students declarative vocabulary to the point where they even use it when writing.

Granted, second language learners need to learn the affectations of colloquial speech - especially in terms of listening skills. However,for them to use such speech in a manner that does not sound stilted, or even silly for that manner, takes years of practice and, more often than not, years of exposure to such language as a resident of the country in question. Idiomatic language can also fall into this
category in that a non-native speaker will often not quite grasp the subtleties of voice differentiation and/or timing necessary to properly reproduce it.

An experienced ESL/EFL teacher will go to great lengths to teach the vagaries of the English language, but must also be keenly aware of the fine line that exists between mastery of the language and using that mastery in a befitting manner.

Well, I really gotta go now; I wanna say more, but dunno if I('ve) got the time.