Higher Urban Charter School Market Share Linked to Lower NAEP Test Scores

With over a decade of data, now can answer quite a few questions about the billionaire-led so-called education reform that has shuttered so many schools, atomized low-income neighborhoods that used to be centered around their local schools, created so much churn in the teaching profession, and turned many urban schools into all-test-prep, all the time.

We can now tell whether students are actually learning more on national tests like the NAEP (National Assessment of Educational Progress) as a result of No Child Left Behind, Race to the Top, and the Common Core.

Along with many other researchers and commentators, I have been showing repeatedly, on this blog, that the answer is, “No.”

My latest piece of evidence comes from two sources: the NAEP Trial Urban District Assessment (TUDA) test scores for 21 urban school systems published by the National Center for Educational Statistics (NCES), and data on the percentages of students enrolled in charter schools in those cities, published by the National Alliance for Charter schools. 

We have been repeatedly told that more charter schools means better education for all; supposedly the competition with the charter schools will cause the regular public school systems to improve dramatically as well.

So if you plot the “market share” of charter schools in a bunch of cities against their NAEP math or reading scores in the 4th or 8th grade, you should see a strong positive correlation, something like the data I invented in the graph below:

hypothetical charter market share vs test score graph 2

Imaginary data showing that higher market share for charter schools (y-axis) is positively correlated to higher NAEP test scores (x-axis)

Well, it happens to be the other way around.

We do not see strongly focused scatterplots with linear correlations going up and to the right.

We instead see strong trendlines going DOWN and to the right.

Yup, for the 17 cities that NAEP TUDA and the National Alliance for Charter Schools both have data, for these 17 large cities, the higher the fraction of charter schools, then the worse the kids in the public schools do on the NAEP in 4th and 8th grade reading and math.

For example:

This greenish scatterplot has the “market share” of charter school students in these 21 cities on the y-axis on the left, and the NAEP grade 4 math average scale score for that entire city along the x-axis on the bottom. It’s quite clear that higher NAEP scores are linked with lower charter school enrollments.

naep 4th gr math vs charter market share


In the graph above, the value of R-squared is 0.454, and the value of R (the coefficient of correlation ) is 0.6738.  For completeness, I also plotted the average score for all US urban students (238) and he average for all US public school students (241). The topmost blue dot on the left represents Detroit, and the next highest dot, at about 43% market share, is Washington, DC. The dot near the bottom center at a NAEP score of 220 is Fresno. The system at the very bottom, with a score of 234, is Louisville KY (aka Jefferson County).

In the next graph (tan/blue), we see the exact same data, only for 8th grade:

naep gr 8 math vs charter market share

In this one, R is almost 0.7, and R-squared is about 0.49, both quite strong correlations.

In the next graph (gray and tan), we see the same data, only for 4th grade reading:naep 4th grade reading vs chaerter market share


The very alert reader may notice that this is the graph that I used to make up some phony statistics that DO NOT EXIST but are predicted by many pundits who haven’t been in a public school classroom for a very long time.

My final graph for today shows the same thing, but for 8th grade reading.

naep 8th grade reading vs charter market share


All of the correlations have been rather strong, but this one is the strongest of all.

Of course, correlation isn’t necessarily causation. We don’t know from the data alone which factor causes the other, or if there is a third factor causing  both changes.

But in any case, the argument that charter schools and choice — as defined by Gates, Wallton, Rhee and Duncan — would inherently lift all boats is definitely demolished.


Unfortunately, we don’t have disaggregated average NAEP charter school scale scores in these 21 cities. Charter schools used to be included in each of the cities’ scores, but in most cases, that reporting stopped in 2009, so we only have the scores for the kids in the regular public schools, not the charters or the voucher or private or parochial students in these cities. (In a previous post, I tried to calculate the charter school NAEP average scale scores for Washington, DC, and they mostly agree with what Erich Martel calculated, but I’m not 100% sure about them yet because I don’t know if private school scores are, or are not,  included with the charter school scores. And I don’t have any data that would allow me to calculate any average charter school scores on the NAEP in any other city on this list.

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One CommentLeave a comment

  1. Isn’t it common sense that the more money you take out of the public schools to fund charters, the less that will be available to maintain programs? There isn’t any outside funding source to replace the teachers and programs that have to be cut. And, given that charters are less likely to serve the neediest populations of students, then public schools are left to educate a higher need population with fewer resources. It is clear that the push to privatize has nothing to do with providing a quality education for all students.


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