A shortage of teachers--or a shortage of good teachers. Either way, it is the reality. And there is a severe shortage of math and science teachers, particularly those qualified to teach physics and chemistry (a lot of administrators make the mistake of assuming a science teacher with a background in biology can march right into a physics class and teach it with no problems).

I think we can agree, though, that it is very difficult to keep the best people in the job. It's simply ridiculous to cast aside teachers' complaints because they supposedly have it so good. If we had it that good, we'd have no problem attracting the best and brightest.