Redistributing highly effective teachers from low- to high-need schools is an education policy tool that is at the center of several major current policy initiatives. The underlying assumption is that teacher productivity is portable across different schools settings. Using elementary and secondary school data from North Carolina and Florida, this paper investigates the validity of this assumption. Among teachers who switched between schools with substantially different poverty levels or academic performance levels, we find no change in those teachers' measured effectiveness before and after a school change. This pattern holds regardless of the direction of the school change. We also find that high-performing teachers' value-added dropped and low-performing teachers' value-added gained in the post-move years, primarily as a result of regression to the within-teacher mean and unrelated to school setting changes. Despite such shrinkages, high-performing teachers in the pre-move years still outperformed low-performing teachers after moving to schools with different settings. (Contains 2 figures, 17 tables, and 11 footnotes.)