I’ll Have a Dose of Confirmation Bias, Heavy on the Bias

(Guest Post by Matthew Ladner)

So how do private school students do in Science compared to public school students.  I wasn’t sure, so I went to the NAEP data explorer to find out.

Private school students outscore public school students, but private school students tend to be more affluent than public school students, and there can be differences in special need and language profiles. Fortunately the NAEP data explorer allows you to take such factors into account.  To maximize the comparison, we will only look at the NAEP science scores of children eligible for a Free or Reduced priced lunch under federal guidelines, and who have neither a special education nor an English Language Learner designation.  This is about as close to apples to apples comparison you can hope for in NAEP data.

So NAEP changed the framework of their Science exam in 2009, making the 2009 and later exams incomparable to those given before 2009. The comparison of general education poor children between public and private schools is sporadically available in both NAEP science frameworks.  You can’t compare old NAEP science to new NAEP science, but you can compare public and private school scores within each year.  So let’s start with 4th grade:

NAEP Science 4


Private school generic poor children outscored their peers in the public schools 2 out of 3 tries. Let’s look at 8th grade scores:

NAEP Science 8

Private school generic poor children outscored their peers three out of four times in 8th grade.  Let’s have a look at 12th grade science:

NAEP Science 12

So for those of you scoring at home, in 8 possible comparisons, private school general education poor children outscored six times.  It was close (within the margin of sampling error) a few times but every time the result was lopsided it was lopsided in favor of the private school children.  Quite frankly science scores should be higher in both public and private schools for low-income kids, but the available evidence does show an overall private school advantage. Unless you happen to be Stephanie Simon working through a sizable case of confirmation bias, in which case this is what you saw:

Taxpayers in 14 states will bankroll nearly $1 billion this year in tuition for private schools, including hundreds of religious schools that teach Earth is less than 10,000 years old, Adam and Eve strolled the garden with dinosaurs, and much of modern biology, geology and cosmology is a web of lies.

Gosh, a billion dollars-that sounds scary! At least until you think of it as less than 80 percent of the Dallas Independent School District’s budget.  Still, this is an outrage! We should put a stop to it immediately!

Except…how is it that these kids at hillbilly flat-earther private schools keep managing to score about the same or more often better than their public school peers on the NAEP Science exams? Does the NAEP science framework ask a battery of questions on the Book of Genesis?  Does learning how to play Duelling Banjos wire the mind for multiple choice science exams?

Um, no. Not so much. Private schools just do a better job teaching science overall.  Ms. Simon has written a hyperbolic story about a crisis that does not exist.  The available evidence suggests that if we eliminated all funding for choice programs that it would result in a net decrease in knowledge of science.

If Ms. Simon wants to pull the funding for private schools based on science achievement, the river needs to flow both ways and we will have to pull the funding for an even larger number of public schools on the same basis.  In the meantime, if Ms. Simon doesn’t like private schools, she always has the option of not enrolling her children in one. As an added bonus, her kids can learn science on Khan Academy if she happens to choose one of the many that do a poor job of teaching science.

11 Responses to I’ll Have a Dose of Confirmation Bias, Heavy on the Bias

  1. George Mitchell says:


    Who determines if a student is eligible for FALS status? My guess is that the data are suspect. Does anyone verify eligibility or is the honor system in place?

    We see, ad nauseum, charts and graphs and tables purporting to show results for such students. But how confident can one be about the data?

      • George Mitchell says:

        Thanks. I thought I recalled something on this. It’s four years old. It’s either unreliable or everyone who uses FALS is lazy and is ignoring it.

      • matthewladner says:

        The data is messy, but no one has developed a better alternative yet.

      • George Mitchell says:

        Unless I am mistaken, “better alternatives” exist but are much harder (and costlier) to implement. The longitudinal study that Pat Wolf, et.al., did of the Milwaukee program had closely matched control and treatment groups. It is troubling that a scholarly journal such as EdNext would surface such questions and then many scholars and others (especially in the media) proceed blithely forward relying on “messy” data. Wisconsin’s education bureaucrats require scrupulous verification on income for choice programs. Yet no one appears to care that much broader programs have few if any requirements.

  2. […] with the Foundation for Excellence in Education, points out that Stephanie Simon suffers from a serious case of confirmation bias. He digs deeper into scores for low income students in private schools versus public schools on the […]

  3. […] with the Foundation for Excellence in Education, points out that Stephanie Simon suffers from a serious case of confirmation bias. He digs deeper into scores for low income students in private schools versus public schools on the […]

  4. […] red herring sensationalism about a “billion dollars for creationism”–which, as Matt Ladner points out, is much less than the entire annual budget for one school district in […]

  5. Ellis says:

    Besides the new “framework” (educators can’t use simple language!), is there an explanation for the reversal in which school tends to do “better”? “Six out of eight” comparisons is fine, but the trend (ignoring the new framework) seems to have been toward public schools doing better. Given the parental involvement (a huge advantage for the scores of private schools) required to enroll a student in a private school, I wouldn’t think that a change in the test would cause the private schools’ to lose ground.

  6. matthewladner says:


    The new framework essentially kills meaningful trend data for the Science exam.

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