The Merit of Assessing Teachers

RALEIGH – My colleagues and I have previously written about the growing mountain of evidence for the proposition that teacher quality is strongly related to student performance, both in the classroom and after graduation. These findings suggest that if North Carolina hired, evaluated, and paid teachers on the basis of performance – as measured by the gains their students make over the course of a year – there would be tremendous educational, fiscal, and economic benefits.

Instead, North Carolina maintains a set of tenure and compensation policies that discourage excellent teaching, reward mediocre teaching, and protect too many awful teachers from being “encouraged” to pursue a line of work more suited to their talents.

Here’s another piece of evidence to add to the pile. Late last year, the National Bureau of Economic Research published a working paper examining the validity of value-added measures as a means of identifying teachers who confer long-term benefits on their students. The three researchers – Raj Chetty, John N. Friedman, and Jonah E. Rockoff – were responding to the common objection that teachers who appear to add value in the classroom may only be inheriting students who, for other reasons, were likely to progress regardless of the quality of the instruction they received.

The researchers found no evidence that value-added assessments were biased by socioeconomic status (SES). Such assessments really do seem to measure the value that individual teachers add to the classroom experience. Furthermore, the study showed that students exposed to high-value-added teachers exhibit remarkable benefits. Here’s the math:

Students assigned to high-VA [value-added] teachers are more likely to attend college, attend higher-ranked colleges, earn higher salaries, live in higher SES neighborhoods, and save more for retirement. They are also less likely to have children as teenagers. Teachers have large impacts in all grades from 4 to 8. On average, a one standard deviation improvement in teacher VA in a single grade raises earnings by about 1% at age 28. Replacing a teacher whose VA is in the bottom 5% with an average teacher would increase the present value of students’ lifetime income by more than $250,000 for the average classroom in our sample.

In a previous column, I related economist Eric Hanushek’s similar thought experiment about what would happen if American school systems replaced the least-effective 7 percent of teachers with those of just average performance:

This seemingly small change would have revolutionary results, by raising the average student performance of America to that of Finland, the highest-scoring country in international tests. “Closing the achievement gap with Finland would, according to historical experience, have astounding benefits, increasing the annual growth rate of the United States by 1 percent of GDP,” Hanushek wrote. “Accumulated over the lifetime of somebody born today, this improvement in achievement would amount to nothing less than an increase in total U.S. economic output of $112 trillion in present value.”

As long as I’m quoting scholars on the subject of teacher tenure and compensation, JLF’s own director of education studies, Terry Stoops, gets the last word:

Value-added analysis has upended the conventional wisdom on teacher quality. For years, public school advocacy groups complained that the most talented teachers snub minority and low-income schools by migrating to less challenging and higher paying schools in culturally and economically homogeneous suburbs.

These facts raise serious questions about the continued use of state salary schedules, which reward teachers based on years of experience, advanced degrees, credentials, or additional duties. Value-added analysis suggests that the current system does not select and reward talented teachers or preclude ineffectual teachers from remaining in the classroom.

In other words, it’s time for a change.

Hood is president of the John Locke Foundation.