DOI: 10.1187/cbe.03-12-0028 †Corresponding author. E-mail address: deallen@udel.edu. I learned that planning a science lesson as a group can be very frustrating as well as very rewarding: Frustrating when I had to suspend certain beliefs that I held about what constitutes a good science lesson in order to really listen to what another member of our group was trying to share.... Rewarding in having the chance to think deeply about what I think is important in planning, assessing, and delivering a lesson, and getting to hear what other people think is important. —A teacher participating in a San Francisco Lesson Study group For >20 yr, the American public has grown accustomed to the drumbeat of bad news about their schools. Poor performance on standardized tests, gaps in achievement between minority and white students, and high student drop-out rates have become part of the modern lexicon. It is clear that the path forward to address these problems should emphasize and reflect the overwhelming importance of effective teaching. There is cogent evidence that a competent teacher, with good quality curricular materials and adequate resources, makes a major difference in student performance on standardized evaluations (Ferguson, 1991; Hammond and Ball, 1997; Wenglinski, 2000). This fact was recognized by the National Commission on Mathematics and Science Teaching for the 21st Century when it stated that, “...the most direct route to improving mathematics and science achievement for all students is better mathematics and science teaching” (U.S. Department of Education, 2000, p.7). Beyond the gloomy numbers in international examinations, which show that students in the United States do poorly in both science and mathematics when compared with students in comparable countries, there is perhaps a silver lining. Researchers are looking closely at the educational cultures of consistently high-performing countries, such as Japan, and asking if there are similarities and differences in approaches, and what aspects of those systems are transferable to our own. What they are finding is perhaps surprising. There are dramatic differences in the methods used by teachers in Japan and their counterparts in the United States. Examination of many hours of videotapes (as part of the Third International Mathematics and Science Study [TIMSS] videotape study project) (Stigler et al., 1999) of mathematics teaching suggests that teachers in the United States are more likely to state concepts directly to students, while teachers in Japan predominantly develop students’ thinking about concepts rather than simply stating the concepts. Teachers in Japan (Stigler and Hiebert, 1999) focus more of their lesson content on what is referred to as “medium or high quality mathematical content” (such as problem-solving strategies), whereas U.S. teachers spend most of their lesson time occupied with “low quality content” (such as repetitive practice). In Japan, a high percentage of lessons include student presentations, whereas in the United States, <10% of 8th-grade lessons involve student presentations. It appears from analysis of Japanese and U.S. educational systems that the difference is not so much in the teacher competence as in the methods that the teachers use. One might argue that teachers transfer to their classroom many of the practices and methods that were used by their teachers. Whether or not that is the case, Japanese school systems, particularly at the elementary grade levels, incorporate a mechanism for helping in-service teachers to incrementally improve their classroom practice. Known as Lesson Study (or jugyou kenkyuu in Japan), it is a mechanism that helps Japanese teachers to improve their practice based on evidence from the classroom. Lesson Study is based on a long-term, continuous improvement model—one that values gradual change built on existing classroom practice. It starts from the premise that the lesson—that is, what happens in the classroom—is critically important. The purpose of Lesson Study is not to produce the “perfect lesson,” but rather to catalyze the process of professional development that occurs when teachers collaboratively reflect on student understanding and the evidence for it, and plan the classroom experience. It is focused on student learning and on the classroom observations, evidences, and student work that reveal the level of success. It is a collaborative process, allowing teachers to engage in a mutually supportive deconstruction of what went right as well as what went