What's this rubbish mean? Don't you realize that Ielts school firstly sends its client schools the teachers' resumes? Secondy, the schools accept or reject said teachers on that basis.
Another point, how do you know the Africans are barely understandable in their work environment, as opposed to native speakers of English? Probably the client schools that accept them do so in the knowledge they are getting a good deal because they're shelling out less to Ielts School, which will mean the Africans are earning less, but the students' English is so pathetic there, so they couldn't appreciate any kind of pronunciation. Incidentally, know you not there are native speakers bred in Tyneside, for example. But nobody except their fellow Geordies can follow what they are saying! Likely they are more difficult to follow than Africans. As an FT, you are so naive that it's unbelievable! [edited]

You're another charming individual are you not "What's this rubbish mean?"

People from Tynside are native-born English speakers, so they can speak however they please. People from Africa(apart from South Africans) are not native-born English speakers; so, should teach Swahili, or whatever Bantu language. Same with Russians; they should teach Russian.

How do I know, Mr Clever Cloggs, how Africans sound in a classroom? Because I have had the misfortune to sit in and listen to them.