With international exams (PISA and TIMSS) producing results every three or four years, there is near continual talk of East Asian dominance in mathematics education. Beyond the reporting of scores, some studies have compared mathematics teaching in these countries with U.S. instruction. However, researchers are not (usually) grade school math teachers and are often interested in different issues and see different things than teachers. In all these discussions of scores and findings, little interaction has occurred between U.S. math teachers and East Asian math teachers, an interaction that could provide another level of insight in these conversations. In this article, U.S. teachers describe effective professional development that they experienced in Japan and how their teaching has been illuminated through continued collaboration with Japanese colleagues.