Tying Teacher Tenure to Student Scores Doesn’t Fly

By Justin Snider

The day we can accurately measure a teacher’s performance has finally arrived. Or so the likes of District of Columbia Schools Chancellor Michelle A. Rhee and New York City Mayor Michael R. Bloomberg would have us believe.

In a speech this past fall in Washington, but directed at the New York state legislature, Mayor Bloomberg praised “data-driven systems,” while arguing that student test scores should be linked to teacher-tenure decisions. His preferred analogy was to medicine: To prohibit the use of student test-score data in such decisions, Bloomberg explained, would be as insane and inane as “saying to hospitals, ‘You can evaluate heart surgeons on any criteria you want—just not patient-survival rates.’ ”

John Merrow, the education correspondent for “PBS NewsHour,” favors instead the swim-instructor analogy : If half the class nearly drowns when trying to demonstrate what they’ve learned, we’d be downright daft not to find...