This study examined whether scaffolded lesson study might contribute to the emergence of a shared professional teaching knowledge culture among 4th grade social studies teachers. The study reports findings from a three-year lesson study professional development project that sought to develop professional teaching knowledge for problem-based historical inquiry among participating teachers. Participants included six 4th grade State History teachers from three different schools and three different school systems. Using qualitative data collected during three yearlong lesson study cycles, we present evidence (...) that suggests that lesson study can be used to develop a shared professional teaching knowledge culture among 4th grade social studies teachers. We suggest, however, that a combination of factors might contribute to variations in teachers' participation in that shared professional teaching knowledge culture including the degree to which the teachers embraced the public nature of lesson study. These factors include the teachers' idiosyncratic views of teaching and learning, the teachers' individual tolerance for socially constructing curricula, and the degree to which teachers acceded to cultural obstacles within elementary schooling. (shrink)