Today I go to take New Mexico's Reading Teacher Assessment. Historically, I am a math and science teacher with a degree in biochemistry and most of my teaching experience in middle school science. This year, I was asked to teach a reading class to students more than 2 years behind in reading. I have mixed feelings, and I know a number of my colleagues blatantly disagree (for my sake as well as for my students' sake) that I teach reading.
My mixed feelings come from the reality that small schools serving primarily low-performing students have an unworkable number of constraints. Special education - including gifted education, intervention classes, and even electives are extremely difficult to successfully provide when 50% or so of your students aren't on grade level. This exact same thing happened in my last school. Based on test data, we were required to provide extra interventions to something like 1/3 of our students. We had to have all these teachers squeeze intervention math and reading classes into their schedules - qualified or not. And I think schools work better when teachers come together to "make it work," even when circumstances are difficult. I hate having colleagues who refuse to put in the extra work, because I often end up being the person who does agree to take on more for the good of the school and the students. I might be making the wrong decision.... me teaching reading might not be for the good of the school or the students. Maybe if I'd said "no," the school would have had to come up with a different, better solution.
I also think that, if someone is a good teacher, they will very likely be a good teacher of any subject. There is always some lag time when building a new curriculum - I'm not on top of my game like I was after teaching and perfecting 8th grade science for 5 years. But I'm also not as bad as some other teachers who allow their students "free time" all the time and don't provide clear instructions or engaging tasks with meaningful objectives. I know how to do all of those things for math and science, and therefore I'm not totally lost when it comes to doing them in reading.
There is more to being "highly qualified" than just taking a test or even taking college courses. It really takes observing a teacher's classroom and the work that students are actually producing in that class....