What is the realation of one's own content knowledge to the ability to teach in that area? Knowing a lot about science, for example, does make a big difference for science teaching. It provides a useful resource for the classroom and confidence for the teacher. But elementary teachers have to teach all the sciences and have little formal training in any of them. Not knowing, and knowing that they don't know, some teachers are naturally discouraged. But no one could know all the sciences anyway, or even all of the one major science secondary teachers are expected to teach. Knowing Science
On the other hand, if a teacher can listen to children, can encourage inquiry, and can bring in what she or he does know, then a lot of learning can occur. Helping students build on their natural curiosity, a teacher can put them on a path to real learning. The teacher who says, "I don't know, but I can work with you to find out," is way ahead of the the one who says, "this is the answer," especially when the actual answer is often more complex and interesting than that given in any beginning text.
Teaching that way requires confidence, and that usually means getting over the sometimes paralyzing belief "I can't teach science because I don't know enough"