Value-Added Confusion in NYC
I'll admit that I myself was poised to blog about the New York Times' finding that teacher quality is widely diffused throughout the citywhich Fordham's Mike Petrilli called "jaw-dropping news." Thankfully a few interviews and deadlines got in the way, and I didn't get to it before Philissa Cramer at GothamSchools roundly exposed that the whole thing is "not really news at all."
The Times article, addressing the much-debated release of 18,000 New York City teachers' value-added scores, states:
[T]eachers who were most and least successful in improving their students' test scores could be found all around؏in the poorest corners of the Bronx, like Tremont and Soundview, and in middle-class neighborhoods of Queens, like Bayside and Forest Hills. They taught in schools in wealthy swaths of Manhattan, but also in immigrant enclaves.
Surprising, huh? Well, no. Cramer explains that the value-added formula in New York controls for differences in student populations, and that by design both effective and ineffective teachers would be found throughout the city. She writes:
The adjustments mean that teachers are effectively ranked relative to other teachers of similar students. Teachers who teach similar students, then, are guaranteed to have a full range of scores, from high to low. And, unsurprisingly, teachers in the same school or neighborhood often teach similar students.
Oops. Kind of like writing a news story about how no students scored above a 2,400 on the SATs ... or how one National League team and one American League team made it to the MLB World Series. ...
That said, it's also indicative of how confused people continue to beed reporters and analysts includedabout value-added methodologies, and how easily published teacher rankings can be misinterpreted.