Measuring the impact of a great teacher

"Value-added" assessment is an increasingly popular method of evaluating the influence of schools and teachers on student achievement. Often, this analysis measures the impact of individual teachers on their students’ standardized test scores, while controlling for factors such as student demographics and test scores from previous years. While local and national education leaders have vigorously debated the significance of standardized testing for many years, a major new report reveals that teachers who perform well in value-added assessments also provide measurable, long-term academic and economic benefits to their students and to society as a whole.

Harvard and Columbia University researchers tracked 2.5 million children from fourth grade to adulthood, assessing the value-added impact of the children’s teachers in grades four through eight and analyzing long-term academic and economic trends. Those who had a high-performing teacher between fourth and eighth grade were found to be more likely to attend college and to earn higher incomes as adults, among other benefits. According to the study, “on average, having such a teacher for one year raises a child's cumulative lifetime income by $50,000.” The difference between having an average rather than low-performing teacher was also found to be significant.

Advocates for value-added assessment have long reasoned that it offers scientific, measurable proof of a teacher’s effectiveness. Many teachers and parents have been less convinced, arguing that it merely shows how effective a teacher is at teaching to the test, which may not have any long-term value. The Harvard/Columbia study may support both sides: while it does not claim that improving test scores alone will produce long-term benefits, it concludes by stating that “good teachers create substantial economic value and…test score impacts are helpful in identifying such teachers.” In other words, teachers who are effective at improving their students’ test scores also are likely to be effective teachers in general, and effective teachers do make a significant difference.

In Wisconsin, with the controversial passage of legislation that strictly limits collective bargaining, many school districts are beginning to redesign their teacher compensation models to emphasize factors related to teacher effectiveness, rather than seniority. Value-added assessment seems likely to be included as a component of some of these new compensation systems.

The Milwaukee Public Schools’ teachers union – which still has a multi-year collective bargaining agreement in place – nonetheless is working with the district to revamp its teacher evaluation system, which will be based partially on student outcomes. MPS officials have been working with UW-Madison researchers at the Value Added Research Center (VARC) for more than 10 years, but this is the first time VARC research will be used in MPS teacher evaluations.

It will be interesting to follow the reaction to the new Harvard/Columbia study as it receives greater scrutiny from academics, education policy-makers and stakeholders. (One critic has already challenged the study's validity, arguing that the students in the study were tested in the early 1990s, before the “high-stakes” eras of No Child Left Behind and Race to the Top.) The report’s conclusion, however, strengthens what we intuitively know about the importance of quality teachers, and it seems unlikely that would be altered by any change in policy.