In Japan, "jugyou kenkyuu"--or lesson study--is the most common form of professional development among elementary school and lower-secondary school teachers. While in the United States it is best known as a means of improving math instruction, in Japan, lesson study is practiced in all subjects, from language studies to physical education. Teachers typically begin engaging in lesson study as part of their preservice training and continue the practice throughout their careers. The goal of lesson study is to engage teachers in a research process that will help them improve their teaching. Lesson study provides a framework for Japanese teachers to think deeply about content and student learning. It also gives them an opportunity to learn from each other. This contrasts sharply with the isolation that so often characterizes teaching in America. A common criticism is that if teachers do not have sufficient content knowledge, their efforts may not be productive. One way to improve the process: draw on experts from the outset, particularly when addressing a concept that teachers and students alike find challenging. The author states that teachers in the United States may need to call on "knowledgeable others" more often than their peers in Japan.