This study by a group of prominent researchers will not be news to teachers and principals, but should be a revelation to the U.S. Department of Education, to Secretary Arne Duncan and to Mayor Michael Bloomberg. Here is the summary.

It says that teacher turnover harms student test scores in both mathematics and reading. It says that it harms academic performance most among poor and black students. It says that high rates of teacher churn affect both the students who lose their teachers and even those who didn’t. The researchers are cautious about why this is so, but they think it may have to do with the continual disruption of the school’s community and culture. It is hard to have collegiality and a cohesive staff when staff members come and go in large numbers.

Good schools don’t have high attrition among teachers and principals. Good schools are schools that professionals feel part of and want to sustain and improve. Churn is not good for schools. And now we know it is not good for children either.

So every time you hear Secretary Duncan laud the “turnaround” model, remember that he is lauding a bad idea. Remember he is saying that the mere act of tossing out the principal and half the staff constitutes “reform.” There may be instances where a school is so bad and so incompetent and so corrupt that a start over is necessary, but those instances are rare. Typically a school with low scores is struggling to meet the needs of children who are poor and don’t speak English; it needs help, not churn-by-design.