Over at the Prichard Committee’s blog, Susan Weston just posted data she worked up for her recent presentation to the Louisville Forum about the condition of Jefferson County’s public schools.

Weston claimed that while Jefferson County’s elementary and middle school students notably lag behind their counterparts in the vast majority of other Kentucky school districts, the “high schools look much healthier.”

Well, that diagnosis may be an uncomfortable forerunner of what is about to happen to real health care in this country. It’s way off. Louisville needs a second opinion.

To begin, Weston looked at test results for the overall student average scores and separately for low-income student scores and for African-American student scores.

Ms. Weston claims that in both reading and math, Louisville’s fourth and seventh grade students lagged behind somewhere between 76 percent to 92 percent of the other school districts in Kentucky depending upon the subject, grade level and student group considered.

That is a pretty low performance level.

In very sharp contrast, she claimed that for 10th grade reading and 11th grade math, only somewhere between 17 percent and 42 percent of the other districts performed better than Jefferson County.

That is a huge difference – making Jefferson County High Schools look like miracle workers.

Can this really be? Naaah.

Weston forgot a good rule with statistics. If things look too good to be true, better check for some hidden explanation.

In this case, it really isn’t hard to understand what is happening.

Very simply, Jefferson County drops out a much higher proportion of its kids than other districts do before those kids ever get to take high school tests. It’s no wonder that the remainder in Jefferson County’s high schools looks like they are doing better – proportionately there are a lot fewer kids left to test than in other districts. And, as dropouts, overall those Jefferson County kids would certainly drag down the averages had they stayed in school long enough to test.

The truth is that while other districts are working hard to keep kids in school, even if they will score low on state tests, Jefferson County has some of the lowest graduation rates in the state in the new 2011 graduation rate report that was released last week by the Kentucky Department of Education (KDE). This table summarizes some of the grim reality in those new graduation rate statistics.

In fact, while the overall statewide graduation rate went UP in the new KDE report from 76.7 percent in 2010 to 78.0 percent in 2011, Jefferson County’s overall high school graduation rate for all students dropped from 69.3 percent in 2010 to the 67.8 percent figure you see in the table above.

Yup – FALLING graduation rates! That’s the stuff that makes for a “healthy” school system – NOT! But, it can inflate high school test scores.