My background is primarily in art, my teaching certification is general elementary, and yet at both of the museum jobs I've had so far I've found myself engaged in science education -- first natural/environmental science, now anthropology, astronomy, and paleontology. Here in the education department at my museum, in fact, many of us are teaching science with liberal arts and/or education backgrounds, rather than hard scientific training. I'd venture to guess there's a similar trend in schools: in the past few years, when I was applying for classroom teaching positions, I was often asked (based, presumably, on my museum ed and office experiences) if I would alternatively consider a science or technology teaching position.
I'm very happy doing what I do, almost certainly happier than I'd be at an art museum. And it seems clear that we need more educators comfortable teaching math and science, and if people with in-depth training in those areas aren't available (because, as I assume, they are going for more lucrative research/corporate/government/ academic jobs? or is there another reason?), surely someone needs to fill that gap. And I personally believe that, at least for grades K-8, it is more important to have smart, enthusiastic educators who can make the material accessible and interesting for their audience than it is to have educators who are necessarily experts in their field. But what do others think? Anyone else out there noticing this trend, or teaching subjects in which they are self-taught?