I saw a commercial bragging that “by *** we will only have native speaker teachers”. In my teaching career, many schools have turned down my application with a simple: “We don’t hire non-native speakers”.
Now, I must say my relation to my mother tongue is different than the one that I have with my “learned languages”. I can give my students insider tips, tell jokes and teach idiomatic expressions on another level. I probably have a better “feeling” for the language itself and can try to offer a taste of it to my class. I can talk about my learning process as a child or my experience with other students… But I will never be aware of the struggles and problems adults might be facing when learning that language, cultural gaps etc. because I have honestly never been there.
Furthermore, I will never have the analytical thinking tools which I have when it comes to teaching foreign languages. I have been forced to have it in order to acquire them. I was in the exact same position as my students are now. I am much more… reliable and relatable. I know where problems could occur, hidden traps, I feel their frustration, I know what is important to get completely right and what you really need to avoid in terms of grammar, semantics or behaviour and which rules and words you do not need and can skip (maybe just for now).
I have a deeper “conscious knowledge”, which is easier to teach than simply “a feeling”. The feeling is there, of course. In the meanwhile, it has become a well “developed” one. But it is still something I have learned and am constantly learning. Thinking of my experience, I feel blessed. As a former Latin and Ancient Greek as well as a linguistics student, I had the luck to be forced to sweat and learn about my mother tongue, too. Nevertheless, I can always rely on the phrase ”It just sounds better/right”. Actually, can I? To be honest, I think it is a VERY dangerous and false sense of security when you want to be a scientist, a proper linguist.… and that is why I rather teach foreign languages (and better) than my own. I would rather question (and allow to be questioned) my German, French, English, Spanish, Ancient Greek, Latin knowledge than my beloved-hated-mother tongue Italian.
So, no matter who you see in front of you, be assured that this person, despite of their mother tongue, can indeed be a good teacher and can have something valuable to add to your language (and life – but this post focuses on language knowledge) experience, something from which during your very own learning process.