In recent years, school districts from New York City to Los Angeles have revamped the way teachers are evaluated and rewarded. In the District of Columbia, teachers voted last year for the option to trade job security for merit pay, meaning that high-performing instructors could expect five-figure bonuses (and the laggards could fear pink slips). One particularly controversial component of D.C.’s move to greater teacher accountability is the use of “value-added” evaluations based on the test scores of students in a teacher’s classroom. New York Governor Andrew Cuomo also took a tentative step into this teacher evaluation minefield when he suggested in his State of the State on Wednesday that New York teachers statewide should be evaluated using standardize test scores. Critics of value-added measures worry that putting so much emphasis on standardized tests will create a culture of “teaching to the test,” and they speculate about whether standardized tests really tell us anything useful about students and whether they’re acquiring the skills they’ll need to lead successful lives.
The findings of a new National Bureau of Economic Research study released by economists at Harvard and Columbia suggest that at least some of these critics’ concerns may be misplaced. By following students in grades three through eight into adulthood, the research team was able to link, for the first time, value added performance evaluations to life outcomes we actually care about. The economists found that teachers who boosted standardized test scores also better prepared their students for later in life: Students who had high value-added teachers in grade school attended college at higher rates (and attended better colleges), were less likely to be teenage mothers, and earned more in early adulthood. High performing teachers may more than justify much higher pay.
Why has the so-called accountability movement been so late in coming to education when we’ve been hearing for decades that our schools are in crisis? Because evaluating teacher performance is difficult. To generate comparable performance metrics for teachers across entire school districts requires going beyond the subjective assessments of principals, administrators, and others. Most schools have come to rely on standardized tests to compare student performance, and these same tests are now employed to evaluate the instructors who teach them.
Of course, evaluating teachers based on the performance of their students is going to reward teachers for securing jobs in places with smart and diligent students, not for effective teaching. For example, Scarsdale students do far better on standardized tests than those in Harlem. This isn’t necessarily the result of higher-quality instruction in Scarsdale schools, but rather because Scarsdale—a high-income zip code known for its schools—attracts families that value education. Even within a single district, some schools naturally attract stronger students than others. If teachers and principals were evaluated based on the level of student test scores as compared to the performance of students in other schools, be they across town or across the country, they’d be tempted to put a lot of energy into luring high-performing students from other schools rather than improving the educations of the students they’ve got.
To get around this problem, teacher performance is gauged instead by measuring how students perform compared to how they performed at the end of the previous school year—this is the so-called value-added approach. If test scores are raised consistently for most students in a teacher’s classroom year after year, we can be pretty sure that it’s mostly because of the teacher. Of course, test score improvements can still be affected by all sorts of considerations beyond the teacher’s control, like class size, a community’s economic ups and downs, and random chance. The value added technique does its best to control for these myriad factors, and to provide some indication of how certain researchers are about whether student improvements resulted from great teaching or just dumb luck.