Fighting for Equity in Education

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Teacher Turnover Harms Student Achievement

Tuesday July 12, 2011

A new study from the United States shows that teacher turnover in schools lowers student achievement, especially for low performing and black students. Students in grades with higher teacher turnover scored lower in both English and mathematics. The study also found that teacher turnover has a disruptive effect on students apart from changing the composition of teacher quality in schools.

The study notes that teacher turnover rates are high, particularly in schools serving low-income, non-white and low-achieving student populations in the US. Nationally, about 30% of new teachers leave the profession after five years, and the turnover rate is 50% higher in high-poverty schools as compared to more affluent ones. Teacher turnover rates also tend to be higher in lower-performing schools.

The study was published by the National Bureau of Economic Research last month. It was based on data for 625,000 4th and 5th grade students across all New York City elementary schools over five academic years. It linked student test scores in math and English to student, class, school, and teacher characteristics.

While the effect of teacher turnover on student achievement in English and mathematics is generally small, it is much larger in schools with higher proportions of low achieving and black students. The harmful effects of turnover on English achievement in these schools were generally two to four times stronger than in schools with smaller proportions of these students. For mathematics, the effects varied from slightly larger to about twice as large.

Much of the existing literature assumes that teacher turnover impacts student achievement by changing the average quality of teachers in schools. For example, student results may decline because higher quality teachers leave and are replaced by lower quality teachers.

The study found that changes in teacher experience explain some of the effect, but also turnover has an impact beyond this change in teacher composition. Its results show that turnover has a harmful effect on student achievement even after controlling for different indicators of teacher quality. Further, the findings indicate that turnover has a broader, harmful influence on student achievement since it can reach beyond just those students of teachers who left or of those that replaced them.

The study says that one possible explanation is that turnover negatively affects collegiality or relational trust among teachers or that turnover results in loss of institutional knowledge that is critical for supporting student learning. It suggests that more research is needed to identify the specific mechanism.

The study concludes with some policy implications of its findings. The harmful effects of teacher turnover indicate that schools would benefit from policies aimed to keep grade level teams intact over time. One possibility might be to introduce incentive structures to retain teachers that might leave otherwise. Implementing such policies may be especially important in schools with large populations of low performing and black students, where turnover has the strongest negative effect on student achievement.

Trevor Cobbold

Matthew Ronfeldt; Hamilton Lankford; Susanna Loeb & James Wyckoff, How Teacher Turnover Harms Student Achievement, Working Paper No. 17176, National Bureau of Economic Research, Cambridge Mass., June.

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