How can this intuition—that better grasp of mathematics would produce better teaching—appear
to be so wrong? KTEM suggests an answer. It seems that successful completion of college course
work is not evidence of thorough understanding of elementary mathematics. Most university mathematicians
see much of advanced mathematics as a deepening and broadening, a refinement and clarification, an extension and fulfillment of elementary mathematics. However, it seems that it is possible to take and pass advanced courses without
understanding how they illuminate more elementary material, particularly if one’s understanding of that material is superficial. Over the past ten years or so, Deborah Ball and others [B1–3] have interviewed many teachers and
prospective teachers, probing their grasp of the principles behind school mathematics. KTEM extends
this work to a transnational context. The picture that emerges is highly instructive—and sobering.
Mathematicians can be pleased to have at last powerful evidence that mathematical knowledge
of teachers does play a vital role in mathematics learning. However, it seems also that the kind of knowledge that is needed is different from what most U.S. teacher preparation schemes provide, and we have currently hardly any institutional structures for fostering the appropriate kind of understanding.