"Don?t think about elephants," skoolboy?s father used to joke, long before George Lakoff?s manifesto with a similar name. The joke, of course, is that by trying not to think about elephants, all that you can think about is elephants. The harder I tried not to think about elephants, the more I thought about them.

The New York City Department of Education has its own variation. This month, the DOE is sending Teacher Data Reports, which purport to estimate the effect of individual teachers ...