That was the conclusion of researchers Sarah and Christopher Lubienski in a study last year of data from the 2000 National Assessment of Educational Progress (NAEP).
Now they're back with similar and more-extensive results in a follow-up study of the 2003 assessment, drawing from a much larger national data sample of 13,577 schools and 343,000 students.
The results, the researchers said, raise further questions about the assumed academic benefits of private, as well as charter, schools. The results also raise doubts about how effectively parental choice can influence school quality.
"The presumed panacea of private-style organizational models -- the private-school advantage -- is not supported by this (NAEP's) comprehensive dataset on mathematics achievement," the Lubienskis, education professors at the University of Illinois at Urbana-Champaign, wrote in a summary of their recent study.
A paper on the study was posted Jan. 23 on the Web site of the National Center for the Study of Privatization in Education (NCSPE) (http://www.
"More and more states are looking at voucher programs, or trying to organize public schools on a private-school model, and this study brings up serious questions about that approach," Chris Lubienski said. "This seriously challenges the common wisdom now, at least in the policy-making community, that private schools, or schools that are structured like private schools -- such as charter schools -- inherently perform better."
The researchers looked at achievement and survey data from NAEP's 2003 national sample of 190,000 fourth-graders in 7,485 schools and 153,000 eighth-graders in 6,092 schools. The schools in the sample were categorized by NAEP as public (non-charter), charter and private, with the private schools broken down further by Catholic, Lutheran, conservative Christian and "other private."
NAEP is considered the only nationally representative ongoing assessment of U.S. academic achievement, and is often referred to as the "gold standard" of school performance data.
NAEP tests for more than just math, but the researchers chose to analyze math achievement because, unlike literacy, it is viewed as being less dependent on a student's home environment and more an indication of a school's effectiveness, Sarah Lubienski said.
As in the previous study, the researchers found what everyone expects when looking just at test scores: Private schools did better than regular (non-charter) publics. "Private schools are always going to do better if you're not controlling for demographic differences," Sarah Lubienski said.
Charter schools scored lower than regular publics in the fourth-grade sample, when looking just at test scores, and about even with regular publics in the eighth grade.
However, when they compared schools with similar student populations, based on students' backgrounds -- a kind of apples-to-apples demographic comparison -- the private schools' advantage disappeared, and even reversed in most cases.
Using a statistical analysis known as hierarchical linear modeling, the Lubienskis found that regular public schools scored "statistically significantly higher" than private and charter schools at the fourth-grade level. With 10 points roughly considered a grade-level difference in achievement, the regular public schools were trailed by 11.9 points by conservative Christian schools, 7.2 points by Catholic schools, 4.2 points by Lutheran schools, 5.6 points by all other private schools, and 4.4 points by charter schools.
At the eighth-grade level, the regular public schools were trailed by 10.6 points by conservative Christian schools and by 3.8 points by Catholic schools.
Lutheran and charter schools led regular public schools by 1.0 and 2.5 points, respectively, and all other private schools were 2.3 points below regular public schools -- but all of these three gaps were determined to be statistically insignificant by the researchers.
To determine differences in students' backgrounds, the researchers used NAEP survey data related to the students' socioeconomic status, which included their eligibility for free or reduced lunch and their access to learning resources in the home, such as books and a computer. The researchers also incorporated survey data on students' race and ethnicity; gender; disability and limited English proficiency.
The Lubienskis thought the gaps between regular public schools and conservative Christian schools were especially significant for any discussion about school choice. "Assumptions that academic quality will be driven by parental choice need to be re-examined in view of the fact that conservative Christian schools, the fastest growing segment of the private school market, were also the lowest performing," they wrote in their summary of the research.
The researchers, who are husband and wife, caution that their conclusions are directed at policymakers rather than parents. They are not telling parents that the local public school is automatically better, any more than the common wisdom should tell parents that a local private or charter school is best. "We could imagine sending our kids to a private school if the circumstances were right," Chris Lubienski said.
They also noted that the NAEP samples for some school types were limited, and cautioned against seeing their research as the last word on the subject. "We don't think this is the definitive answer on this issue, but I do hope that it would put the brakes on -- at least in people's minds -- about this rush to privately run schools," Chris Lubienski said.