Teachers raise their game when the quality of their colleagues improves, according to a new study offering the first-ever evidence to document a "spillover effect" in teaching.
Authors C Kirabo Jackson and Elias Bruegmann based their findings on an analysis of 11 years of data on North Carolina schoolchildren. The study is due to be published in October in the American Economic Journal: Applied Economics, a peer-reviewed journal.
The authors and independent experts said the study results were important, because they had implications for school staffing practices and merit pay for teachers.
Mr Jackson, an assistant professor of labor economics at Cornell University in Ithaca, New York State, said rewarding teachers at the school level, rather than as individuals, would "foster feelings of team membership, and that increases the incentive to work together and help each other out."
Studies outside education have long shown that effective workers can have a spillover effect on their colleagues. Supermarket checkers, for instance, work faster when they are in the line of sight of a productive colleague, and berry-pickers tend to calibrate their speed to that of friends laboring nearby.
Until now studies have not noted the same pattern in teaching, in which it has long been thought that peers work mostly in isolation.
For their study, Mr Jackson and Mr Bruegmann focused on mathematics and reading test-score data for students in third through fifth grades(P5-6), most of whom would have had the same teacher for all their core academic subjects. They measured teacher quality in two ways: by tracking "observable" characteristics, such as whether teachers were experienced or certified, and by calculating how effective teachers were at raising the test scores of their students. The latter, a "value-added" calculation, was figured using data from teachers' previous students.
Either way, the researchers found, student achievement rises across a grade when a high-quality teacher comes on board. The study also discovered that good teachers seem to have the most impact on beginning teachers.
"He (Mr Jackson) has some pretty good evidence, as good as you can get in an observational study, that when a good teacher shows up in your grade it seems to have a positive impact, and that impact stays around," said Douglas O Staiger, an economics professor at Dartmouth College in Hanover, New Hampshire.
Mr Jackson said the new peer-effects findings raise questions about the way schools are staffed, particularly urban schools. "A lot of beginning teachers end up in inner-city schools and move to suburban districts," he said.
"Sending the teachers who need the most guidance to be surrounded by teachers who are the least well-equipped might be a problem. We need to make sure we have some high-quality teachers in inner-city school districts."
This is an edited version of an article for the American journal Education Week.