Students who have even one above-average teacher between the fourth and eighth grades are more likely to attend college and to earn more money later in life, according to a new study that analyzed data on more than a million students. “This work provides more robust evidence that teachers really do matter long-term and that we can identify who good teachers are,” says economist Raj Chetty of Harvard University, who was not involved in the research.
Good teachers produce successful students. The mantra makes sense, but it’s been hard to establish scientifically, says economist Gary Chamberlain of Harvard University. In the new analysis, Chamberlain used data from more than 800 schools in a single large urban area in the United States. (The city and all personal information on the students and teachers are being kept under wraps so that no one can be identified.) The data set, which spanned 1988 through 2009, included information on classroom assignments and test scores in grades four through eight, and—for those who attended elementary school in the early part of that range—the students’ later college attendance and their earnings at age 28.
Other researchers, including Chetty, had previously used the same data set to conclude that teacher quality influenced students’ test scores  and that those test scores could then predict the students’ college attendance and earnings in adulthood. But Chamberlain wanted to apply a different mathematical approach to verify the findings and ask another question: Do teachers have an effect on these long-term outcomes beyond their influence on test scores? So he developed a new model to compare different classrooms within the same school and different classes run by the same teacher.
When Chamberlain crunched the numbers, he found that some teachers consistently produced students that went on to college and that the effect of the teachers was even stronger than simply their impact on test scores . If teachers are given quality rankings based only on their students’ test results, an above-average quality teacher bumps up a student’s chances of college attendance by less than a quarter of a percent. But if teacher rankings are instead based on the longer-term data, a high-quality teacher sends nearly 1% more students to college.
The difference between the two ranking scenarios, Chamberlain says, is likely due to teacher attributes that are not reflected in standardized test scores; they give the students untested skills that help them thrive. Like other studies, Chamberlain’s work found that teachers had an effect on annual earnings at age 28—the increase hovered around 1%. Over time, those numbers add up—in terms of the effect that a single teacher has over his or her career, and in terms of the effect of many good—or bad—teachers in a row on a student.
“This is additional evidence that teachers matter,” Chamberlain says. “And we’re getting closer to figuring out what the ingredients of teacher quality are.”
The study, published today in the Proceedings of the National Academy of Sciences, doesn’t have the data to delve deeper into what these ingredients are, he says. But future work could try to answer why teachers have such a long-lasting impact by looking at other ways of gauging teacher quality, such as evaluations. And researchers are still trying to determine whether some of the apparent effect of teachers can instead be explained by other social and economic qualities of students, such as the education level of their parents.
“The challenge is that students are not assigned randomly to teachers,” Chetty says. Some teachers might repeatedly get assigned more children who have had difficulties in the past, whereas others might get classrooms full of children with parents who are highly involved in their children’s education and request that teacher, he says. “In those cases, you’re going to see big differences in outcomes that have nothing to do with the teachers.”
For now, Chamberlain doesn’t expect the new numbers to influence policy on how teachers are evaluated. But he hopes that the findings motivate others to work toward studying what makes a good teacher have such long-lasting effects. “Some school districts are interested in using these measurements of teacher value to make personnel decisions on hiring and promotions,” Chamberlain says. “But we still need to pin down exactly what observable things about a teacher matter for their effects on students.”