EWA’s 66th National Seminar, held at Stanford University, took place earlier this month. We asked some of the journalists attending to contribute posts from the sessions. The majority of the content will soon be available at EdMedia Commons. Over the next few weeks I’ll be sharing a few of the posts. Melissa Bailey of the New Haven Independent is today’s guest blogger.

When a school loses a high percentage of teachers, what happens to the kids they leave behind?

A researcher shed light on that question, and a former teacher shared a solution, at a EWA National Seminar panel on teacher turnover.

The researcher, Susanna Loeb of the Stanford Graduate School of Education, said the teacher turnover problem has been well-documented: One in three teachers leaves the profession within five years.

Common sense would say that turnover hurts kids, but Loeb said surprisingly little research has been done to test that assumption. She and her co-authors tackle the question in a paper published in the American Educational Research Journal in February. The title: “How Teacher Turnover Harms Student Achievement.” (Read it here.)

Turnover is complicated, she said: Whether it’s good or bad depends on the composition of the workforce—whether the teachers who come in are more effective than the ones who leave. The disruption itself may also be good or bad: It may lead to innovation, but it can also make it harder for teachers to coordinate among themselves, as new teachers have to be trained and socialized.

Previous studies had shown schools with high turnover tend to have lower student performance, but there was no causal connection between the two, Loeb said. Looking for a causal tie, Loeb’s group examined 850,000 observations of students in the 4th and 5th grades of New York City schools over an eight-year period. They looked at the percentage of teachers who left the school, and how students fared on tests in the following year.

Loeb sought to answer the question: “Do students do worse in the year after there is high turnover?” Her answer was yes: Teacher turnover hurt student achievement in English and math. The effect was significant—about as significant as the effect of free lunch eligibility (a standard measure of poverty) on test scores, she said. The effect was strongest among schools with more low-performing and black students.

What’s more, she reported, turnover appeared to have a ripple effect throughout the school.In schools with high turnover, achievement suffered even for kids in classrooms where the teachers stayed.

Loeb said the research leaves a few questions to be explored: How can schools reduce turnover? Why do teachers leave? And how can schools buffer against the disruptive effects of turnover?

Anthony Cody—who taught for 24 years in Oakland public schools—gave an on-the-ground solution to Loeb’s first question, drawn from his experience working in a school with a significant turnover problem. Two to three of 10 science teachers would leave every year.

The high turnover took its toll on the experienced teachers who saw new teachers come and go, he said. When a new teacher would join the school, veteran teachers would “assess their likelihood of survival, like birds in a nest. If one looks weak, you don’t feed that one—you only give the food to the one who’s going to make it.”

Cody created a new mentoring program called Team Science that paired experienced science teachers with rookies. The school built a “family” feeling within the department. The initiative cut turnover to zero within the department, he said.

Cody, who has blogged about teacher turnover at Education Week, argued that some districts get into a “bad addiction” by turning to programs like Teach For America to fill vacancies. The programs bring in new teachers who don’t tend to stick around, he said, so, two years later, the school is left back at square one.

Moderator Francisco Vara-Orta of the San Antonio Express-News said the topic is ripe for stories. He dug into some data and found that charter schools in his region were shedding teachers at a rate more than three times higher than regular public schools.

Jessica Williams of The Lens in New Orleans asked about the sustainability of charter schools where teachers stay up all night working. Loeb said some charter schools like KIPP make it easier for teachers to work there for short periods of time. That’s not good, Loeb argued: “Our goal in reform should be to stabilize schools that serve low-income kids.”

“We don’t want a system where poor kids get turnover and middle-income kids don’t,” she said. “That’s just not the right answer for the country.”