New York City's schools chancellor, with the support of Mayor Bloomberg, wants to release the value-added test score results for 12,000 teachers - revealing for parents and the public the student learning gains attributable to each instructor. News organizations have requested the data; the city is ready to comply. The city's United Federation of Teachers has challenged the release, and a judge will decide next month. I've spent many years looking carefully at such data. I know it can be incendiary; I know it has flaws.