Fuzzy Math The guesstimate that struck down California’s teacher tenure laws.

http://www.slate.com/articles/business/moneybox/2014/06/judge_strikes_down_california_s_teacher_tenure_laws_a_made_up_statistic.html



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.”