Want to Ruin Teaching? Give Ratings AS the founder of a charter school network in Harlem, I've seen firsthand the nuances inherent in teacher evaluation. A few years ago, for instance, we decided not to renew the contract of one of our teachers despite the fact that his students performed exceptionally well on the state exam. We kept hearing directly from students and parents that he was mean and derided the children who needed the most help. The teacher also regularly complained about problems during faculty meetings without offering solutions. Three of our strongest teachers confided to the principal that they were reluctantly considering leaving because his negativity was making everyone miserable. There has been much discussion of the question of how to evaluate teachers; it was one of the biggest sticking points in the recent teachers" strike in Chicago. For more than a decade I've been a strong proponent of teacher accountability. I've advocated for ending tenure and other rules that get in the way of holding educators responsible for the achievement of their students. Indeed, the teachers in my schools - Harlem Village Academies - all work with employment-at-will contracts because we believe accountability is an underlying prerequisite to running an effective school. The problem is that, unlike charters, most schools are prohibited by law from holding teachers accountable at all. But the solution being considered by many states - having the government evaluate individual teachers - is a terrible idea that undermines principals and is demeaning to teachers. If our schools had been required to use a state-run teacher evaluation system, the teacher we let go would have been rated at the top of the scale. Education and political leaders across the country are currently trying to decide how to evaluate teachers. Some states are pushing for legislation to sort teachers into categories using unreliable mathematical calculations based on student test scores. Others have hired external evaluators who pop into classrooms with checklists to monitor and rate teachers. In all these scenarios, principals have only partial authority, with their judgments factored into a formula. This type of system shows a profound lack of understanding of leadership. Principals need to create a culture of trust, teamwork and candid feedback that is essential to running an excellent school. Leadership is about hiring great people and empowering them, and requires a delicate balance of evaluation and encouragement. At Harlem Village Academies we give teachers an enormous amount of freedom and respect. As one of our seventh-grade reading teachers told me: "It's exhilarating to be trusted. It makes me feel like I can be the kind of teacher I had always dreamed about becoming: funny, interesting, effective and energetic. Some of the new government proposals for evaluating teachers, with their checklists, rankings and ratings, have been described as businesslike, but that is just not true. Successful companies do not publicly rate thousands of employees from a central office database; they don't use systems to take the place of human judgment. They trust their managers to nurture and build great teams, then hold the managers accountable for results. In the same way, we should hold principals strictly accountable for school performance and allow them to make all personnel decisions. That can't be done by adhering to rigid formulas. There is no formula for quantifying compassion, creativity, intellectual curiosity or any number of other traits that make a group of teachers motivate one another and inspire greatness in their students. Principals must be empowered to use everything they know about their faculty - including student achievement data - to determine which teachers they will retain, promote or, when necessary, let go. This is how every successful enterprise functions. A government-run teacher evaluation bureaucracy will make it impossible to attract great teachers and will diminish the motivation of the ones we have. It will make teaching so scripted and controlled that we won't be able to attract smart, passionate people. Everyone says we should treat teachers as professionals, but then they promote top-down policies that are insulting to serious educators. If we don't change course in the coming years, these bureaucratic systems that treat teachers like low-level workers will become self-fulfilling. As the great educational thinker Theodore R. Sizer put it, "Eventually, hierarchical bureaucracy will be totally self-validating: virtually all teachers will be semi-competent." The direction of education reform in the next few years will shape public education for generations to come. Secretary of Education Arne Duncan has repeatedly said that in the next decade, "over 1.6 million teachers will retire," and our country will be hiring 1.6 million new teachers. We will blow that opportunity if we create bureaucratic systems that discourage the smartest, most talented people from entering the profession. Deborah Kenny is the chief executive and founding principal of Harlem Village Academies and the author of "Born to Rise: A Story of Children and Teachers Reaching Their Highest Potential."