Berger's office also pointed to a new study by researchers from Stanford and the University of Virginia into performance incentives work introduced in the Washington, D.C., schools in 2009-10. "The evidence available to date has been mixed at best" as to whether performance pay works, Profs. Thomas Dee and James Wykoff wrote. But the researchers said poorly performing teachers left Washington classrooms in greater numbers under threat of dismissal, while teachers who stayed showed improved performance.