Teachers are systematically sorted across schools. Often, schools serving the lowest-achieving students staffed by the least-skilled teachers. While teachers' school preferences account for some of the sorting, school practices are also likely to be a key factor. The authors examine the relationship between a school's effectiveness during a given principal's tenure and the retention, recruitment and development of its teachers. Three key findings emerge about principal effectiveness. More effective principals: (1) are able to retain higher-quality teachers and remove less-effective teachers; (2) are able to attract and hire higher-quality teachers to fill vacancies; (3) have teachers who improve at a greater pace than those in schools with less effective leadership (there is some evidence for this, albeit weak). These findings drive home the importance of personnel practices for effective school leadership.