By DAVID LEONHARDT
The education research of recent years has pointed overwhelmingly to the importance of teachers. Perhaps more than anything else – quality of principal, size of school, size of class – the strength or weakness of classroom teachers influences how much students learn and even how they fare later in life.
The great unknown is how to improve teacher quality, be it by attracting more good teachers, weeding out more bad teachers or helping teachers become better at their craft.
A new study, released on Thursday, offers powerful if still tentative evidence that teacher-evaluation programs can play an important role. The study is especially notable because past research about evaluation programs suggested they had little effect. The new paper, however, studies an evaluation program – called Impact, in the District of Columbia school system – that is far larger, with bigger rewards and stiffer penalties, than most programs.
Impact, which began under Michelle Rhee while she was chancellor, has been a hotly debated program, and the new study is sure to attract attention from both supporters and critics of teacher evaluation. New York state’s plan to begin evaluating teachers has also been the subject of intense praise and criticism, as have such programs elsewhere.
The study found that Impact caused more low-performing teachers to leave the school system than otherwise would have been expected. The program also seemed to improve teaching quality – as measured by classroom observations and test scores – of teachers with both strong and weak evaluation scores.
“High-powered incentives linked to multiple indicators of teacher performance can substantially improve the measured performance of the teaching work force,” conclude the researchers, Thomas Dee of Stanford University’s Graduate School of Education and James Wyckoff of the Curry School of Education at the University of Virginia. Evaluation programs, they add, can bring “substantive and long-term educational and economic benefits” both by “avoiding the career-long retention of the lowest-performing teachers and through broad increases in teacher performance.”
The study has not yet undergone peer review. It is being published as a working paper by the National Bureau of Economic Research, a Cambridge, Mass., group run by some of the country’s top academic economists.
The Impact program differs from some other teacher-evaluation programs in significant ways. While others offered bonuses of several thousand dollars for high performance – up to $3,000 in New York City and up to $6,000 in a Texas district, for example – Impact’s bonuses reached as high as $25,000. Teachers who were judged as “highly effective,” which translated into being in roughly the top 16 percent, in two consecutive years did even better: they received raises that lifted their base pay by almost 30 percent over the next 15 years.
Impact also applied to most of the District of Columbia’s school system, meaning it received far more attention than the smaller pilot programs put in place elsewhere. And Impact’s evaluations for most teachers were based largely on classroom observations that measured how well teachers followed so-called best practices. Test scores played only a secondary role for most teachers, along with principals’ assessments of the teachers’ contributions to the entire school. Mr. Dee and Mr. Wyckoff speculate that using classroom observations may have a larger effect on teachers, because they can more easily control their own teaching style than they can influence their students’ test scores.