Jordan Weissman, a business correspondent for Slate, read the Vergara decision and noted that the judge’s conclusion hinged on a strange allegation. The judge quoted David Berliner as saying that 1-3% of the teachers in the state were “grossly ineffective.” The judge then calculated that this translated into thousands of teachers, between 2,750 and 8,750, who are “grossly ineffective.”

Weissman called Professor Berliner and asked where the number 1-3% came from. Dr. Berliner said it was a “guesstimate,”

He told Weissman, “It’s not based on any specific data, or any rigorous research about California schools in particular. “I pulled that out of the air,” says Berliner, an emeritus professor of education at Arizona State University. “There’s no data on that. That’s just a ballpark estimate, based on my visiting lots and lots of classrooms.” He also never used the words “grossly ineffective.” And he does not support the judge’s belief that teacher quality can be judged by student test scores.

Dr. Berliner mailed Weissman a copy of the transcript to show that he did not use the term “grossly ineffective.”

Weissman then called Stuart Biegel, a law professor and education expert at UCLA, to ask him “whether he thought that the odd origins of the 1–3 percent figure might undermine Treu’s decision on appeal. Biegel, who represented the winning plaintiffs in one of the key cases Treu cited, said it might. But he thought that the decision’s “poor legal reasoning” and “shaky policy analysis” would be bigger problems. “If 97 to 99 percent of California teachers are effective, you don’t take away basic, hard-won rights from everybody. You focus on strengthening the process for addressing the teachers who are not effective, through strong professional development programs, and, if necessary, a procedure that makes it easier to let go of ineffective teachers,” he wrote to me in an email.”