I don't want to take up any more space on Edwize...
And here's what the Bureau of Labor Statistics has to say on the issue:
Currently, many school districts have difficulty hiring qualified teachers in some subject areas—mathematics, science (especially chemistry and physics), bilingual education, and foreign languages. Qualified vocational teachers, at both the middle school and secondary school levels, also are currently in demand in a variety of fields. Specialties that have an adequate number of qualified teachers include general elementary education, physical education, and social studies.
Blogs are indeed a place to express your opinion, but it bothers me when people proclaim "facts" without any sort of reference to back them up. Opinions or guesses can be described or disclaimed as such, but if you say something as though it were gospel-truth, you make a better case if you can prove it.
In my experience (see how easy it is to make a disclaimer before stating your opinion?), many math & science teachers just starting out in the profession have a hard time calibrating their expectations to what their students can realistically produce. They tend to have had extremely good math & science educations themselves, and math & science usually came easily to them, so they hit a wall when they find that their students struggle more than they did. This was true of me during my first year of teaching: What? You don't know that in eighth grade??? How is that possible? Some people learn ways to help the students achieve, but others just kind of throw up their hands and blame the kids. I have seen this phenomenon in at least three or four new math and science teachers whom I have worked with in six years of teaching, nearly all of whom have left the profession. They have a rough time of it, and then they think about their options and head for med school or banking or computer programming or whatnot. I think that many of them did not consider teaching as a profession until just before entering the profession, whereas many English and SS teachers have had teaching on their list of career options for quite some time, giving them time to get perspective on what the career is like. Again, this is just my hypothesis, based on anecdotal evidence.
What would help? Well, in the NYC schools, a science teacher quickly gets the idea that science is scarcely valued. You don't get a lot of PD and your mentor may or may not be a science teacher. Your school often does not have resources that allow you to teach real science lessons. Fixing these problems might help new science teachers feel less frustrated. It would be great to have a support system to help you learn how to have high expectations without being unrealistic, and how to craft lessons to get basic ideas across without dumbing them down.