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Harvard study shows that teacher quality affects student outcomes

Nearly everyone has an anecdote about the teacher that made a difference to them: the person who taught iambic pentameter or quadratic equations, but also inspired and imparted wisdom. But does teacher quality really matter, or do we simply have fond memories of our mentors?

The answer to the question may seem obvious — how could the quality of a teacher not be critically important to students? But even as education policies target teacher quality, the true effect of having a great teacher, versus a merely average one, have been difficult to assess.

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“It’s very plausible that teacher quality matters; there’s nothing very surprising about that,” said Gary Chamberlain, an economist at Harvard University. “But it’s been extremely hard to document for quite awhile.”

In a study published in the Proceedings of the National Academy of Sciences on Monday, Chamberlain analyzed data from an unidentified large urban school district and found that middle-school teachers could have a small, but real influence on whether people attended college and how much they earned at age 28. His study doesn’t allow him to identify the factors that made one teacher better than another, but instead show that increasing teacher quality significantly, say from the 50th percentile to the 84th percentile, increases the likelihood a child will attend college by nearly one percentage point. Such an increase also adds to annual income by nearly $200 — an increase of about one percent.

Chamberlain said that’s a powerful effect, for just one teacher and one class to have on any child’s future trajectory. But there are factors he can’t control for -- in the study, he was able to rule out the possibility that parents’ income levels were playing a role in the difference, but couldn’t rule out that education levels might help account for the difference. He also said there is a “sorting” problem, in which higher caliber students might end up in certain classes with certain teachers, and future research would be needed to try and rule out the possibility that this selection played a role.

In some ways, this type of economics research doesn’t answer the question everyone cares about most: what makes a good teacher? How can we select the right people and train them to have the best effects on children. But Chamberlain says the type of research he is doing can establish just how powerful having a good teacher can be. That knowledge could help focus policies and reforms on the interventions likely to have the most potent effects.

Carolyn Y. Johnson can be reached at cjohnson@globe.com. Follow her on Twitter @carolynyjohnson.

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