Perhaps this data dump was the best thing to happen to those who have been trying to steer the national school conversation away from testing and more testing, to thinking and learning how to learn. What should be central in all these stories is the fundamental problem: What’s the best way to evaluate teachers? How can authentic learning be measured? Should standardized tests be used at all to do it? They are one-day snapshots of how well one student answers a handful of basic, low-level questions. At best they are crude instruments; at worst, they are vulnerable to manipulation.

Sarah Wysocki’stale from the nation’s capital shines a cautionary headlight on the real-life dangers that may lie ahead for districts that put a lot of stock in these numbers. In DC, value-added numbers count for a full half of a teacher’s evaluation, even more than in New York. Bill Turque reported in The Washington Post that the highly regarded fifth-grade teacher received a stellar review by her principal and peers, and was then fired because so many of her students didn’t show any progress on their math and reading tests last year.

Wysocki offered a new twist on the data troubles. She pointed out to Turque that about half her students arrived in her fifth grade class with what she believed were inflated scores from their previous school—a school that is now under investigation for test tampering. Any honest teacher could never hope to improve on fraudulent scores. She appealed her dismissal, lost, and moved away.

Back in my own journalism class, I decided to walk through some of the teacher data online to see what we could learn. World Journalism Preparatory High School, in Flushing Queens popped up on the screen, a small, energetic 6th through 12th grade school that my students have become very familiar with since it opened in 2006. The DOE gave it a “B” grade this year on its controversial School Report Cards, and past years’ numbers have shown steady improvement. Its’ graduation rate is better than the average high school’s; its’ Regents English scores are above average. But the teachers? According to the clumsy measures, they ranked among the very worst in the city. Of course, it was hardly possible that all the children were teaching themselves.

Principal Cynthia Schneider has learned to ignore these spreadsheets over the last three years. “It’s not good data. It’s bad data, and we know it,” she said. “We know what we’re doing here.” The school had to send only eight kids to summer school last year to catch up, she said. The high school is ranked number 41 in the city. Still, her students and teachers suffered the indignity of a front-page article in the hyperlocal Whitestone Times—a photo of the school, plus the poor teacher rankings. Reporters did not call her for comment.

“I’m all about trying to get a handle on matching student achievement to teacher effectiveness. That’s a good thing,” said Schneider. “But that’s not what this does. At all.”

The data? Clear as mud. And now just about everybody in New York and beyond knows it.

LynNell Hancock is the H. Gordon Garbedian Professor of Journalism at Columbia, and director of the school's Spencer Fellowship in Education Journalism.