The authors assert that lesson study--a collaborative, teacher-led approach to learning from practice--offers a deeper, broader, more sustainable method of improving teacher practice than one-on-one coaching does. In lesson study, teachers and coaches of all levels of experience can work together, each bringing his or her own professional questions to the work. Thus, lesson study can accommodate differences in expertise without fixing any group member in the role of "expert" or "novice." In addition, lesson study offers a structure in which coaches themselves can actively engage with current curriculum and standards and thus continue to grow as learners. The authors, all of whom are involved with the Silicon Valley Mathematics Initiative, give examples of how lesson study is woven throughout the initiative's work. (Contains 2 figures and 2 endnotes.)