One of the uphill battles I have faced most of my professional career is the oft-spoken sentiment that really anyone can teach elementary school math since it is so elementary and the math cannot possibly be that difficult. Perhaps this is the primary reason why the US has never truly embraced reform in math education. Perhaps this is a more plausible reason than the oft blamed "new math" of the seventies as to why there is constantly such a strident call for "back to basics" math education. Sometimes my professional life seems like one of failure and futility!
The unbelievably sad thing is that we now know so much about how children and students of all ages learn math much of which is, sadly, not applied in schools or in classrooms where children need it the most. We now know that learning to count, for example, is an extremely complex activity in which children pass through several stages using different forms of number before, if they are lucky, they have developed a secure sense of numeracy by the end of first grade. It takes a skilled, knowledgeable teacher to provide students with activities, guidance and practice with this pedagogical content knowledge. It also takes a skilled, knowledgeable teacher educator to teach teachers the many diverse aspects of teaching elementary school math. For example, do you realize that when you count ,say five objects, with a young child, your voice goes down automatically when you say the number "five" while it goes up with 1,2,3 and 4. If you know this is how we develop the sense of cardinality in children you are a much better parent or teacher than if you do it without realizing what you are doing.
There is so much to know about math education and the way children think mathemtically.