One Year With a Bad Teacher Costs Each Student $50,000 in Lifetime Earnings

Photograph by Ringo Chiu/Corbis

In a landmark ruling, a Los Angeles superior court judge on Tuesday struck down key elements of California’s teacher tenure statutes after finding that the near inability to fire ineffective teachers disproportionately hurts poor and minority students. The ruling rests in large part on what Judge Rolf Treu called ”compelling” academic research that “shocks the conscience.” Highly ineffective teachers, the evidence suggests, can cause lasting harm that reaches far into a student’s future. ”Based on a massive study, Dr. [Raj] Chetty testified that a single year in a classroom with a grossly ineffective teacher costs students $1.4 million in lifetime earnings per classroom,” Judge Treu wrote in his 16-page decision (pdf).

That 2012 study, by Harvard’s Raj Chetty and John Friedman and Columbia’s Jonah Rockoff, analyzed data from 2.5 million kids over two decades, matching test scores with the tax data for the same students and their parents. They tried to isolate how much any individual teacher adds or detracts by comparing how the students scored on end-of-year tests to how similar students did with other teachers, controlling for a host of such things as test scores in the prior year, gender, suspensions, English language knowledge, and class size.

They then checked the predictions made by those models to see if the models reflected some other kind of bias and found that them to be highly reliable. For example, the researchers looked at what happened when teachers left or joined a school and found that, when the model predicted an educator to be great, she in fact immediately improved test scores in her class compared with how students previously performed in that grade.

The academics also found that teacher quality has a lasting impact. Replacing a teacher from the bottom 5 percent of the cohort with an average teacher increases the lifetime earnings of a single student by $50,000. (Spread across an entire classroom, those lost lifetime earnings total $1.4 million, Judge Treu’s headline number.) A truly great teacher, someone in the top 5 percent of a cohort, can increase a child’s lifetime earnings by $80,000, improve the likelihood of college attendance, and reduce the odds of teenage motherhood.

Judge Treu also cites testimony from another Harvard researcher, Thomas Kane, who applied Chetty’s model to the Los Angeles Unified School District. Kane’s 2013 analysis, which was presented at the trial (pdf), looked at several years of data as teachers moved between schools and found that Chetty’s model could accurately identify ineffective teachers and the impact they had on their students’ test scores. Kane found that students “who are taught by a teacher in the bottom 5 percent of competence lose 9.54 months of learning in a single year compared to students with average teachers,” the judge noted in his ruling.

The judge combined those academic findings with those of the state’s own expert, who testified that as many as 3 percent of California teachers—8,250 in all—are “grossly ineffective.” Taken together, the judge found 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.”

The teachers union questioned the outcomes of both studies, saying they blamed teachers for the disadvantages of working in challenging neighborhoods. In the end, Treu was swayed. In essence, he ruled that the state’s constitution guaranteed not just equal access to education but also equal access to quality education, which at its heart, he said, is about great teaching.

    Before it's here, it's on the Bloomberg Terminal.