John Thompson: Why Raj Chetty Is Wrong
John Thompson, historian and teacher in Oklahoma, has reviewed the work of economists Raj Chetty. You may recall that Chetty, a Harvard professor, was co-author of a study that purported to show that teachers could be evaluated by the test scores of their students. An effective teacher, one who raised test scores, would raise lifetime income, increase high school graduation rates, prevent teen pregnancies, and have lifelong effects on students. Raj and his colleagues John Friedman and Jonah Rockoff were cited on the first page of the New York Times(before the study was peer-reviewed), appeared on the PBS NewsHour, and were hailed by President Obama in his State of the Union speech in 2012. Their study became the #1 talking point for those who thought that using test scores–their rise and fall–would be the best way to identify effective and ineffective teachers. As Professor Friedman told the New York Times, “The message is to fire people sooner rather than later.”
Critics thought the findings were fairly modest. Even the Times said:
The average effect of one teacher on a single student is modest. All else equal, a student with one excellent teacher for one year between fourth and eighth grade would gain $4,600 in lifetime income, compared to a student of similar demographics who has an average teacher. The student with the excellent teacher would also be 0.5 percent more likely to attend college.
That works out to about $105 a year for a 40-year career, or $2 a week. But the Times then looked at the results in the aggregate and calculated that the aggregate of gains for an entire class would be $266,000 over the lifetimes of the entire class, or millions of dollars in added income when multiplied by millions of classrooms. Pretty great stuff, even though it means only $2 a week for one student.
The Obama administration bought into the Chetty-Friedman-Rockoff thesis whole-heartedly. Fire teachers sooner rather than later. Use test scores to find out who is a great teacher, who is a rotten teacher. It all made sense, except that it didn’t work anywhere. The scores bounced around. A teacher who was great one year was ineffective the next year; and vice versa. Teachers were rated based on the scores of students they never taught. Tests became the goal of education rather than the measure. It was a plague of madness that overcame public education across the land, embedded in Race to the Top (2009) and certified by Ivy League professors.
Thompson writes:
As it becomes more clear that value-added teacher evaluations are headed for the scrap heap of history, true believers in corporate reform continue to respond with the same old soundbites on the ways that their statistical models (VAMs) can be valid and reliable under research John Thompson: Why Raj Chetty Is Wrong | Diane Ravitch's blog: