It’s trite, but an essential component of a good teacher is deep knowledge of one’s subject matter. The old saying, “Those who can, do; those who can’t, teach,” is not only offensive to the dedicated, overworked and underpaid professionals who work day in and day out in classrooms around the world; it is also wrong.
Of course there are some people standing in front of students with no right to be where they are. Some people go into teaching because they think they will get summers off and only work 6 hours a day. Others went into teaching with a sense of purpose but were worn down by years of disrespect and are now just biding their time until they can collect a pension from the school district.
But the vast majority of teachers I have met (and I have met a lot over the last several decades) care immensely about their students as well as their subject matter. They have more education (minimum of a bachelors degree, but most have masters degrees and many have doctorates) than the general population. They have studied their subject matter AND child development. They have chosen their profession because they earnestly believe that young people are worth teaching, that the future of our nation depends on having educated residents who know how to think critically about the world.
What differentiates a good teacher from another subject matter expert, however, is that she also has what is called pedagogical content knowledge. This is essential–a teacher may not have complete knowledge of her subject, but she needs to know how to convey what she does know to her students in ways that will allow them to learn the concepts and understand them.
I think language teachers may be more maligned than most, in part because of the way that language in general, and bilingualism even more so, are not valued in the United States. Further, language learning is often considered (in the popular mindset) as something that anyone can do, as long as you have exposure. Thus, this belief goes, anyone who speaks a language can teach it, without any particular preparation. This phenomenon may account in part (combined with a general American fear of foreigners, especially those who want to settle permanently in the US) for English language development is relegated to teachers who don’t have any particular preparation for teaching language. ELD is tasked with the massive feat of teaching newcomers survival English, teaching longterm residents academic English, and preparing all of these students for the challenges of mainstream content classes.