My parents and most of my family work in education, so I've been surrounded by educators my entire life. Everyone has to work up the ladder and most teachers do this during their education, whilst they are in college. Some do it after college, once they find a place to teach. But being an assistant is a pre-requisite for most schools who aren't in desperate need of full-time educators.
I personally don't think you need to be an "expert" to each core/basic grammar school curriculum.
I personally don't think you need to be an "expert" to each core/basic grammar school curriculum.