Teachers’ credentials are irrelevant to language learning in my view. A teacher needs to have strong verbal skills, be competent and have experience as a language learner and teacher. School administrators, and education authorities, and the teachers themselves, love credentials. If kids aren’t learning, then they think the answer  just to raise the credential requirements and put on more training. Yet education outcomes do not depend on credentials. There is research that proves it. Good teachers can have a major influence on learners but their credentials are no indicator of their ability as teachers, in my experience.