Let me stipulate from the start that this post is not about selective charter schools. It is, instead, about those charter schools that are supposed to be providing a broader alternative to our “failing public schools.”

From Chicago comes the following data. At the city’s charter schools in 2012-2013, 307 students were expelled. At the city’s public schools, 182 students were expelled. The proportion is even more dramatic when one considers that enrollment in the charter schools is about 50,000 while enrollment in the public schools is over 350,000. So, in the charter schools, about 61 students were expelled out of every 10,000 enrolled, whereas in the public schools, only about five students were expelled out of every 10,000 enrolled.

If charter schools were being presented as a much more selective alternative to the public schools, these numbers would be, perhaps, more understandable and acceptable. But when the charter schools are being presented as simply a blanket alternative to the public schools, these numbers should be very disturbing.

If the most salient evidence of the perceived failure of the public schools in poor urban districts is the declining graduation rate, then expelling more students would seem only to be making that problem worse. But, if expelled students are excluded from the data on graduation rates, because their failure to graduate is a result of their irresponsibility and not some quantifiable inadequacy of the education that they have received, then a reason for the disparity in rates of expulsion becomes much clearer.

If you are trying to educate students whose backgrounds and current circumstances make them very challenging to educate, then one way of improving a school’s perceived performance is to cull the students with whom you are least likely to have success, who are most likely to fail.

But it goes even further than that. In Wisconsin, a study titled “Habitual Truancy and School Report Cards in Milwaukee Schools” has shown that, among factors affecting standardized test scores, “habitual truancy” is by a wide margin the most significant factor, with the experience of teachers ranking a distant second in its impact on scores.

Moreover, the study shows that the average performance on standardized tests of students in charter schools has been greatly enhanced by the aggressive expulsion of students who are classifiable as “habitual truants.”

Worse, the average performance on standardized tests of students in the public schools has been significantly decreased not only by much lower expulsion rates for the students most at risk of dropping out, but also by those schools absorbing many of the at-risk students who have been expelled from the charter schools.

Indeed, given that the performance on standardized tests of students enrolled in charter schools is often not much better, if any better at all, than that of the public school students, one wonders what the average scores would look like if the charter schools were committed, as most public schools are, to the education of all students, including those most challenging to educate.