In a blog post for The Brown Center on Education Policy, Thomas Kane proposes a new definition for an "effective" teacher: one whose "predicted impact on students exceeds that of the average novice teacher."

The former director of the Gates Foundation's Measures of Effective Teaching project, Kane says that one of the advantages of his proposed definition is it clarifies the trade-offs involved in retaining or replacing staff members. He writes:

...it makes explicit the decision a principal implicitly makes every time he or she retains a non-probationary teacher—to forego the opportunity to recruit a novice teacher as a replacement. Would an NFL coach give up a future draft pick for an experienced player he expects to perform worse than the average rookie? Not if he were trying to win. Would a principal promote or retain a teacher with expected performance below that of the average novice? Not if he or she had the students interests at heart.

A commenter on the post makes another sports comparison: "Seems to be the educational equivalent of WAR (Wins Above Replacement)." For those not familiar with WAR (like me before a bit of Googling), it's a way to calculate a baseball player's worth by determining how many more wins he would contribute to a team than would a replacement-level player—someone just up from Triple-A. ESPN now includes the wonky calculation on its stat pages.

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