Concern about students' writing skills has led to recommendations that elementary teachers receive more professional development in how to teach writing (National Commission on Writing, 2006). However, there is currently little evidence about the knowledge teachers need to teach writing well, and it is therefore difficult for teacher educators to design effective professional development experiences. What is needed is a better understanding of the knowledge base that informs teaching writing to elementary children. One possible means of gathering evidence about this knowledge base is through a collaborative teacher research process known as lesson study (Hiebert, Gallimore, & Stigler, 2002; Lewis, Perry, & Murata, 2006). Lesson study engages teachers in planning, evaluating, and improving lessons, so the process generates knowledge teachers find useful for their practice and may provide a mechanism for identifying some of the knowledge needed to teach writing. The goal of this study was to explore that possibility by describing the knowledge about writing instruction that elementary teachers generated through the lesson study process. This qualitative case study drew on complexity theory (Davis & Sumara, 2006), to conceptualize lesson study as a knowledge producing process and the lesson study groups who participated as knowledge producing systems. It addressed two main questions: (1) How did the lesson study systems enable and constrain the knowledge about writing instruction that emerged through them? and (2) What was the nature and content of the knowledge about writing instruction that emerged through the lesson study systems? Four lesson study groups, two in each of two elementary schools, participated. Data was collected through videotaping the lesson study sessions, collecting the documents the groups created during the lesson study process, and interviewing the participants after the lesson study cycle ended. The findings indicated that instances of over constraint, under constraint, and enabling constraint occurred in each lesson study group and that the groups produced knowledge that varied in content and nature. In general, instances of enabling constraint produced knowledge that fit the criteria for professional knowledge outlined by lesson study proponents (Hiebert, Gallimore, & Stigler, 2002). Instances of over constraint and under constraint produced knowledge that did not fit the professional knowledge criteria. This knowledge may therefore be less useful for teachers outside the lesson study groups than for the teachers who generated it. The findings suggests that lesson study can, but does not always, produce knowledge suitable for the professional knowledge base for teaching writing. The implication is that, if lesson study groups are to generate knowledge for the knowledge base, they must be organized is such a way that they prompt enabling constraint within themselves. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]