Teachers are generally recognized as the schooling factor accounting for the highest proportion of student learning outcomes (Aaronson et al., 2007; Hanushek, 1986). This implies the quick and dramatic improvement in school performance observed in turnaround (TA) schools was associated with a major change in the performance of its teachers. This change could be manifest in one of two ways--either the teachers in the school dramatically improve or previously ineffective teachers are replaced with effective teachers. This paper seeks to understand how each of these potential changes in the school's human capital stock contributed to turnaround in Florida and North Carolina. Specifically, the study investigates the following research question: is the improved achievement observed in successful turnaround schools most strongly associated with workforce "development" or "turnover" (or, some combination of the two)? The results suggest TA schools improved through a combination of improving the stable teachers who had been in the school even when it was performing poorly and bringing in relatively effective talent into the school. Recommendations and limitations based on findings are also presented. Appended are: (1) References; and (2) Tables and Figures. (Contains 2 tables.)