There's a more subtle problem too. Very often people chosen as dedicated math teachers (and chemistry teachers, in my experience) find the introductory levels of their subject almost instinctive. They have a hard time understanding why others struggle with the concepts, so they don't know how to help the students struggle through to comprehension.

I can't tell you how many times my college-level biology students come into class complaining about how hard it is to understand the concepts in the math class they've just come from. If I have a few minutes before class, I'll go over how the quadratic equation came to make sense to me, or how multiplication of fractions came to make sense, or how integral calculus or polar coordinates ...or any of a number of other concepts. Usually after my explanation of how I struggled through to a very practical, non-abstract way of looking at those concepts, my biology students' mouths are open in a big "O" of realization... and they get excited again about understanding math.

We need more math and science teachers who struggled with the subject themselves and came to an understanding that can be related to ordinary students.