Should secondary teachers have to pass a subject knowledge exam before being allowed to teach that subject?

I once had a teacher who taught history but didn't realise that the nazi party wasn't around during WWI. She didn't last long and was sent back to the PE department.

I can see how that would make sense for maths. But then asking someone who doesn't have at least an A level in maths to teach maths at secondary would, I think, be extremely dangerous to a school given how performance measures are done.

But English Lit? I can imagine a situation where a teacher has to teach a book or a Shakespeare play they haven't previously studied formally. So would you want to examine subject knowledge or skills ability? Similar for a History teacher who maybe studied European 20th Century and then has to teach American West. Is it the subject knowledge or the skills you want to test? (Though maybe this is just a side question).

In general, I don't really see how it benefits a school long term to employ an incompetent teacher (whether through lack of subject knowledge or teaching ability). I can see it would be cheaper and plus a short term hole, but longer term there would be failed exams, failed Ofsteds and falling roles (and therefore falling income), wouldn't there?

At least lower down a school, would it be better to have a good Geography teacher teaching History by staying one page ahead of the class, of a less good person with a degree in History?

Ideally you have good qualified teachers all being paid decent money with fewer teaching hours, with exams fit for purpose for both bright, middle and low achiever kids. And the moon would be made of cheese and pigs will fly

I think it depends on year group, subject, and area of the subject.

For example, a Year 7 group will only just have come from primary, where it is considered totally normal for a child to be taught History / Geography / RE by non-specialists. Someone who has a good knowledge of the Y7 curriculum in many of these subjects, and decent pedagogical skills, even if they don't have wider subject knowledge, may well do an OK job.

Higher up the school, and for certain 'skills' subjects, I would say not. I would count 'skills' subjects as being things like Maths, Art, PE, Music - where simply knowing and imparting 'content' is not sufficient because the learner has to 'do something' (over and above fact organisation) to apply the skills to the task in front of them.

Of course deep subject knowledge, teamed with excellent teaching skills, is the best combination. However, the importnce of deep subject knowledge does vary with subject and age group, IMO ... but then, I am a generalist primary teacher, so i would say that!