Photograph Credit; GuidoVrola; iStock
By Jordan Weissmann | Originally Published at Slate. June 12 2014 |

The amazing, completely made-up statistic a judge used to strike down teacher tenure in California

This week Los Angeles Superior Court Judge Rolf Treu handed the education reform movement a stunning legal victory, when he struck down California’s teacher tenure laws for discriminating against poor and minority students. The statutes made it so onerous to fire bad teachers, he wrote, that they all but guaranteed needy kids would be stuck in classrooms with incompetent instructors—rendering the laws unconstitutional.
As evidence, Treu cited a statistic that sounded damning: According to a state witness, between 1 and 3 percent of California’s teachers could be considered “grossly ineffective.” Here was the passage:
There is also no dispute that there are a significant number of grossly ineffective teachers currently active in California classrooms. Dr. Berliner, an expert called by State Defendants, testified that 1 to 3% of teachers in California are grossly ineffective. Given that that the evidence showed roughly 275,000 active teachers in this state, the extrapolated number of grossly ineffective teachers ranges from 2,750 to 8,250. Considering the effect of grossly ineffective teachers on students … it therefore cannot be gainsaid that the number of grossly ineffective teachers has a direct, real, appreciable, and negative impact on a significant number of California students, now and well into the future for as long as said teachers hold their positions.
This seemed like a fairly important piece of the decision—if you’re going to argue in court that a state law is dooming children to second-rate educations, you ought to be able to quantify the problem. Politically, it also seemed liked a pretty awful indictment of the state government if officials knew for certain that so many useless teachers were lounging around California’s classrooms. But where did this number come from?
Nowhere, it turns out. It’s made up. Or a “guesstimate,” as David Berliner, the expert witness Treu quoted, explained to me when I called him on Wednesday. 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.”

The expert cited in the ruling doesn’t even necessarily believe that low test scores qualify somebody as a bad teacher.

The phrase appears to have been Treu’s shorthand to describe teachers whose students consistently perform poorly on standardized tests. But Berliner is a well-known critic of using student test scores—or “value-added models,” in the parlance of education experts—to measure teaching skills. In part, that’s empathyeducates – Fuzzy Math – The Guesstimate that Struck Down California’s Teacher Tenure Laws: