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A new study focusing on pairs of identical and fraternal twins in Florida schools bolsters a growing body of evidence on the importance of good teachers.
For the study, which was published last week in the journal Science, researchers from Florida State University in Tallahassee drew on data for a racially and ethnically diverse group of more than 800 pairs of twins in 1st and 2nd grade classrooms across the state. Among identical twins with different teachers, the study found, those whose teachers were judged to be more effective in teaching reading tended to have higher scores on tests of oral literacy than siblings with less effective teachers.
Looking at both the fraternal and the identical twins, the researchers also found that there was more variation attributable to genetics among the twins in higher-achieving classrooms than was the case in classrooms with lower average achievement. According to the researchers, that suggests that teachers play a role in “moderating” students’ achievement—helping them, in other words, to grow to their full potential.
“I don’t want to give the impression that a high-quality teacher will get all children miraculously to a high level of reading,” said lead author Jeanette Taylor, an associate professor of psychology at FSU. “But a teacher provides a supportive environment for the individual differences that kids are already bringing to that environment.”
In education, a handful of studies in recent years have drawn on “value added” calculations of students’ learning gains to measure the impact of good or bad teachers. Critics have argued, though, that those studies don’t always adequately account for unmeasured differences in classes of students when the school year begins.
By studying twins growing up in the same homes, though, researchers are able to eliminate some other factors, such as genetics or parents’ wealth, that might explain differing rates of academic growth among students. Identical twins share 100 percent of their genes, according to the study, while fraternal twins share half.
Nature vs. Nurture
“That’s exactly how I think twins should be used,” said Eric Turkheimer, a professor of psychology at the University of Virginia in Charlottesville, who has also used twin studies to evaluate the effect of educational interventions. “Not so much for the old business of computing what percentage of reading ability is ‘genetic,’ but as little mini-experiments giving us insight into the effects of environmental interventions like teaching, while controlling for everything that identical twins share.”
“It is a way of approximating in humans something that is ordinarily impossible: random assignment of students to teachers, which if it were possible would be a way to demonstrate the effects of teaching definitively,” he said.
By comparing the fraternal and identical twins, researchers were able to assess the extent to which students’ genetic tendencies were able to come to fruition with skilled teachers. A good analogy, Mr. Turkheimer said, would be to think of seeds bred for different genetic traits, such as height or size, that are growing in different soils. All of the plants grown from seeds growing in poor soil would be stunted, while the plants in richer soil might be both taller and more varied.
To measure teacher quality, the researchers tested twins’ classmates in both the fall and the spring on standardized oral-literacy tests, which measure the number of words students pronounce correctly in a set period of reading aloud. For the smaller group of the identical twins, the gains ranged from learning 11 more words per minute by the end of the year to as many as 124 words.
FSU’s Ms. Taylor said the teachers’ effect sizes did not appear to be as large, however, as some of those reported for the studies relying only on value-added analyses of students’ test scores, some of which have found that the academic edge for students with the most effective teachers can amount to as much as a year’s worth of learning.
Even so, said Adam Gamoran, a professor of sociology and educational policy studies at the University of Wisconsin-Madison, the findings “strengthen the importance of the arguments for teacher effectiveness and suggest that value-added analyses might be on the right track.”
Conducted out of the university’s Florida Center for Reading Research, the study was funded by the National Institute on Child Health and Human Development, part of the National Institutes of Health.
A version of this article appeared in the April 28, 2010 edition of Education Week as Twin Study Bolsters Arguments for Good Teachers