i also heard the similar case fr my friend.....her son go to one Central learning center for study English lesson around 3 mths, her comments is the native teacher always change, right now is the 3rd different teacher......when she asked the reason ....the learning center said the teacher had the VISA problem....so sounds not good....
My female Canadian teacher taught my kid for two years and always changed the time, lots of excuses. They don't think this is a problem. A lot of my friends also have similar problem. You have to tolerate.
Hearing all the bad experience of foreign teacher, I feel I am really lucky to find a very good English Native teacher to teach my daughter.
She has been teaching my daughter since P.4, focusing on writing and speaking. My daughter will be going to F.1 this September and we can see her with lots of progress. Even the teacher is prasing on her good writing skill and accurate accent. She has been admitted to a very good secondary school this year.