Scholars have proposed that "the path to change in the classroom lies within and through" more collaborative professional communities among teachers (McLaughlin and Talbert, 1993: 18). How do different approaches to developing collaborative professional communities impact experienced teachers and their ability to change? This article identifies differences between "teacher professional communities" and "professional learning communities". It then presents two case studies to explore the implications of these differences for experienced teachers engaged in school reform. Interview and observational data from two sites suggest that schools which nurture collaborative "teacher professional communities" over time can create resources that help experienced teachers to change aspects of their work. Such resources include: norms promoting innovation; widely shared objectives; trust; continuity with the past; respect for experienced teachers; and traditions promoting morale. Schools that rapidly engineer a "professional learning community" may lack such resources, reducing experienced teachers' willingness and ability to change. (Contains 1 table and 2 notes.)