A new study by three economists suggests that elementary- and middle-school teachers who help increase their students' standardized-test scores have a significant, positive and lasting impact on those students' lives in the long term. Their influence extends beyond academics, as good teachers also mean "lower teenage-pregnancy rates and greater college matriculation and adult earnings," writes the New York Times. The study tracked the lives of 2.5 million students over 20 years, "allowing for a deeper look at how much the quality of individual teachers matters over the long term."
Although the economists set out to challenge the use of value-added ratings, which according to the Times "measure the impact individual teachers have on student test scores," researchers ultimately found that "controlling for numerous factors, including students’ backgrounds...the value-added scores consistently identified some teachers as better than others, even if individual teachers’ value-added scores varied from year to year." They concluded that "using value-added scores would lead to fewer mistakes, not more."

And the positive effect of teachers who increased student test scores was striking. The Times notes, "Replacing a poor teacher with an average one would raise a single classroom’s lifetime earnings by about $266,000, the economists estimate. Multiply that by a career’s worth of classrooms." The researchers surmise that the same results would be obtained by replacing an average teacher with an excellent teacher: "Given the difficulty of finding, training and retaining outstanding teachers...the difference in long-term outcome between students who have average teachers and those with poor-performing ones is as significant as the difference between those who have excellent teachers and those with average ones."

The positive effect of an excellent teacher on one individual student is less impressive than that teacher's potential impact on the entire class taken together, of course. "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." Still, "students with top teachers are less likely to become pregnant as teenagers, more likely to enroll in college, and more likely to earn more money as adults."

The study will likely add fuel to the value-added score debate, as many people--and teachers' unions--"say that isolating the effect of a given teacher is harder than it seems, and might unfairly penalize some instructors." The researchers of this study are firmly on the other side: "The authors argue that school districts should use value-added measures in evaluations, and...remove the lowest performers." One of the researchers, Harvard Professor John N. Friedman, was quoted in the Times as saying, “The message is to fire people sooner rather than later.”