"they are purging nonperforming students at an alarming rate"

(This post also appears at Education and Statistics.)

Mike at ScienceBlogs has some thoughts about selection by attrition:

A letter to Diane Ravitch from a Los Angeles school prinicipal documents just how dishonest and harmful this practice is (italics [Mike's]):

I received an email from Dr. DeWayne Davis, the principal of Audubon Middle School in Los Angeles, which was sent to several public officials. Dr. Davis said that local charter schools were sending their low-performing students to his school in the middle of the year. He wrote:

"Since school began, we enrolled 159 new students (grades 7 and 8). Of the 159 new students, 147 of them are far below basic (FBB)!!! Of the 147 students who are FBB, 142 are from charter schools. It is ridiculous that they can pick and choose kids and pretend that they are raising scores when, in fact, they are purging nonperforming students at an alarming rate--that is how they are raising their scores, not by improving the performance of students. Such a large number of FBB students will handicap the growth that the Audubon staff initiated this year, and further, will negatively impact the school's overall scores as we continue to receive a recurring tide of low-performing students."

Ravitch concludes:

Doing better than an under-resourced neighborhood school is not the same as getting "amazing results." Very few charters do. Probably less than 5 percent. Charters are not a silver bullet. They are a lead bullet. Their target is American public education.

This is just par for the course for modern conservatism: have private systems skim the cream, and leave the public sector to clean up an impossible mess. When they can't, this supposedly shows the inability of government to solve problems.

I have a few points to add:

1. This is a brutal way to treat these kids. You build their hopes up, then crush them, then dump the kids in a new school in the middle of the year;

2. We are talking about getting an influx of students who are badly behind and who are ready to give up and/or act out. This will disrupt classes slightly less than having a nearby car alarm go off at random times once or twice an hour;

3. But I think Ravitch overstates the case against charter schools. I've dealt with some small, independent schools that have impressed the hell out of me and I can see them playing an important role in our system, though a radically different role than Arne Duncan sees.