New performance evaluation systems being adopted in school districts across the country are heralded as long overdue. But there's one aspect that is downplayed by reformers: they give principals a rare opportunity to kill two birds with one stone. Their prey are veteran teachers who are at the top of the salary scale and who are likely to speak out on issues affecting their school because they have tenure. By rating them as ineffective, principals can get rid of them, in the process improving the district's balance sheet and silencing opposition.

Reformers will argue that the scenario I outlined is farfetched. They say that principals wouldn't resort to this tactic. But as I've written before, principals in even the best schools have used their power to settle old scores. The situation at Brooklyn Technical, one of New York City's elite high schools, was a case in point ("Bully on the Wrong Side of the Principal's Desk," The New York Times, Dec. 21, 2005). The presence of teachers unions is no assurance of protection against such abuses, particularly today when budget concerns are so pressing.

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