Who is the language teacher who’s never heard their students say:
“I don’t know why, but I can understand everything my teacher says but when somebody else speaks I can’t understand a word.”
The reason is that teachers develop their own “Teaching English” language – let us call it Teacherese – we simplify our explanation, translate, mime, draw, look up a better explanation/ word definition in a learners’ dictionary – so that students will be able to grasp whatever we’re trying to teach. We tend to speak way more slowly with a clear intonation while also projecting our voice. No wonder students can understand “everything” we say.
The Bible in the Book of James chapter 3 verse 10 implies that our tongue has the power to bless and also the power to curse”. Could it be that in our desire to help our students we end up hampering their language learning skills?
Yes and no. We do help them better understand the language and help students to get a positive and clear example on pronunciation. Teachers could avoid too much of a grammar load – we love saying “that’s an adverbial clause” and expect students to know what we’re talking about, on the other hand so grammatical terms distinguishing an adverb from an adjective will be quite useful when students need to produce language.
Considering the importance of the teacher, it would be advisable he introduced a segment in his class for “mumble time” when he would speak at a more natural way Or introduce to students other English speakers ( if not in person, at least via audio) where they’d be able to identify and assimilate different sounds and accents. 
So fellow teacher warriors, use your skills to bless and not curse your students.
Shine on.
cheers
Mo
The Americanoid Blog 