Abstract: Analyzing existing teacher survey data, this study focuses on the reasons why teachers leave charter schools. The authors found that while overall attrition rates fluctuate from year to year and state to state, as many as one in four charter school teachers leave each year. The single background characteristic that strongly predicted teacher attrition was age: younger teachers in charter schools were more likely to leave than older teachers. Another strong predictor was grade level taught, with attrition rates highest in the upper grades. Attrition was higher for non-certified teachers. The authors recommend that charter school supporters focus efforts on reducing teacher attrition.