While it is widely acknowledged that classroom practice is shaped by its context, the dynamics of that shaping remain elusive. This study conceptualizes the ways in which changing social conditions and national priorities enter into US curriculum practice. Initially, the focus was on the US Census 2000 results showing an increasingly diverse population. After 2001, the terrorist attacks and subsequent events came to overshadow most others. US secondary-school social studies and English teachers were interviewed about changes in their teaching and their reasons for any changes. It was found that social climates do shape curriculum practices but not directly, to the same extent, or in the same manner across classrooms. External trends and events interact with local school conditions and teacher biographies in a historically situated network of mediations. (Contains 8 notes.)