For those interested, here's more from the Times magazine today on assessing teachers by the value they add to students by applying test score progress to a statistical formula. It's a balanced look.
Inevitably, such evaluations will be a part of assessing teachers. But even supporters of it recognize shortcomings in the formula, the difficulty of applying simple ratings to the big group of teachers that don't fall at the extremes and the question of whether every score should be publicized. For example
Value-added data is not gospel. Among the limitations, scores can bounce around from year to year for any one teacher, notes Ross Wiener of the Aspen Institute, who is generally a fan of the value-added approach. So a single year of scores — which some states may use for evaluation — can be misleading. In addition, students are not randomly assigned to teachers; indeed, principals may deliberately assign slow learners to certain teachers, unfairly lowering their scores. As for the tests themselves, most do not even try to measure the social skills that are crucial to early learning.
The value-added data probably can identify the best and worst teachers, researchers say, but it may not be very reliable at distinguishing among teachers in the middle of the pack. Joel Klein, New York’s reformist superintendent, told me that he considered the Los Angeles data powerful stuff. He also said, “I wouldn’t try to make big distinctions between the 47th and 55th percentiles.” Yet what parent would not be tempted to?
And more on public rankings:
Rob Manwaring of the research group Education Sector has suggested that districts release a breakdown of teachers’ value-added scores at every school, without tying the individual scores to teachers’ names. This would avoid humiliating teachers while still giving a principal an incentive to employ good ones. Improving standardized tests and making peer reports part of teacher evaluation, as many states are planning, would help, too.
But there is also another, less technocratic step that is part of building better schools: we will have to acknowledge that no system is perfect. If principals and teachers are allowed to grade themselves, as they long have been, our schools are guaranteed to betray many students. If schools instead try to measure the work of teachers, some will inevitably be misjudged. “On whose behalf do you want to make the mistake — the kids or the teachers?” asks Kati Haycock, president of the Education Trust. “We’ve always erred on behalf of the adults before.”