I continue here in showing you the results of my calculations for how the charter school students and regular public school students in Washington, DC have been faring on the National Assessment of Educational Progress, or NAEP, since the 1990s.

Some of my previous columns were quite simple: I just cut and pasted graphs from the NAEP and NAEP TUDA results, or asked the built-in software for how white, black, hispanic, special education, or free/reduced-price-lunch kids did at the 4th and 8th grade in math and reading.

If you look at my previous graphs, you will notice that, on the whole, the trends AFTER 2007, when Michelle Rhee was installed as the very first DC chancellor, looked just about the same as the trends BEFORE that date.

Today, I did a little math to figure out how black fourth-grade charter school students did in math in DC, in comparison with their counterparts in other large cities, in the nation as a whole, and in the regular DC public schools.

The math goes like this: I figure that the DC state weighted average for any given group or grade level (say, 4th grade African-American students taking the math NAEP) equals the weighted average for regular DCPS at that grade level, times the enrollment at that grade level, plus the product of the charter school weighted average score at that grade level and the charter school enrollment at that grade level; all of that divided by the total enrollment.

Or, if Q = DC state average. and R = DC regular public school weighted average, and V = DC regular public school enrollment, and S = DC charter school weighted average, and W = DC charter school enrollment, and X = V + W = total enrollment in publicly-funded schools in DC, both regular and charter, then

Q = (R*V + S * W) / X

And since I could find everything except S in the literature, then I could simply solve for S. My result:

S = (X*Q – R*V)/W.

And here are my results:

My conclusions?

For black students at the 4th grade in math, the post-Rhee trends in the charter schools are about the same as the trends in DC public schools were BEFORE Rhee was appointed. However, it looks like the trends overall in the regular public schools seem a bit worse.

If past trends had continued, and Michelle Rhee had not become chancellor, the overall educational results might have been very similar to what they are today — inequalities and inequities of course included, because we have lots of that here in Washington, DC.

By the way, if anyone finds a mistake in my work, please let me know by leaving a comment.