Without intentionally doing so, Daniel Willingham gives us another reason why teacher education is important. His most recent post The subtle work of designing instructional materials reports on a paper that discusses the challenges of designing instructional materials. The post points out that an instructional designer must take into consideration how children "consume" information to design learning materials that are not only effective, but visually appealing as well. While I think this is important, I think the concluding paragraph is the most important part in the post.
"On the one hand you could see this as small potatoes--kids will get over it, they will learn how to read graphs. But on the other hand, why knowingly put a stumbling block in front of kids trying to learn math? And more important, how many other small stumbling blocks are there that we don't know about?"
What if you're unaware of the stumbling blocks? This is one function of a teacher preparation program and one that I believe my institution does very well. Our elementary and middle/secondary programs prepare future teachers to anticipate "student thinking" and design lessons accordingly. This is certainly not something individuals intuitively know...it has to be taught.
Still think anyone can teach? Ask them if they know common misconceptions children have about fractions or better yet see how many of these questions they can get right.