Do principals fire the worst teachers?

"This paper takes advantage of a unique policy change to examine how principals make decisions regarding teacher dismissal. In 2004, the Chicago Public Schools (CPS) and Chicago Teachers Union (CTU) signed a new collective bargaining agreement that gave principals the flexibility to dismiss probationary teachers for any reason and without the documentation and hearing process that is typically required for such dismissals. With the cooperation of the CPS, I matched information on all teachers that were eligible for dismissal with records indicating which teachers were dismissed. With this data, I estimate the relative weight that school administrators place on a variety of teacher characteristics. I find evidence that principals do consider teacher absences and value-added measures, along with several demographic characteristics, in determining which teachers to dismiss"--National Bureau of Economic Research web site.