The study looked at the effect of IMPACT, a performance assessment
and incentive system introduced in schools in Washington, DC. IMPACT
evaluates all teachers every year based on multiple measures of
effectiveness (eg, clearly described standards, several teacher
observations by different observers, and student outcomes). Teachers
receive one of four ratings – highly effective, effective, minimally
effective, or ineffective. Those rated ineffective (or minimally
effective two years running) were dismissed. Total teacher turnover
rates in the schools were higher (18% per year) than in similar
non-participating schools (8-17%). Turnover rates among low-performing
teachers (minimally effective or ineffective) were 46%, and for
high-performing teachers (effective or highly effective) 13%.
The study found that there was a small increase in student
achievement in mathematics (effect size of +0.079) that was
statistically significant, and a smaller increase for reading (+0.046)
which was not statistically significant. Turnover of high-performing
teachers had a negative but not statistically significant effect on
student achievement in mathematics (-0.055). Turnover of low-performing
teachers improved student performance in mathematics (+0.21) and reading
(+0.14).
The authors conclude that under a robust system of performance
assessment, turnover of low-performing teachers can generate meaningful
gains in student outcomes, particularly for the most disadvantaged
students.
Source:Teacher Turnover, Teacher Quality, and Student Achievement in DCPS (2016), The National Bureau of Economic Research.