The belief that private schools are inherently better is questioned by a surprising new study. When students' socioeconomic status is taken into account, math scores are better at public schools.

Private schools have a long reputation for outperforming those run by the states. But the new research suggests that might be the case in part because of the caliber of kids who get in.

The research analyzed standardized math scores in more than 1,300 public and private schools.

"If you look at kids of equal socioeconomic class, the kids in public schools are outperforming the equivalent kids in private schools," said Sarah Lubienski, co-author of the study and an education professor at the University of Illinois at Urbana-Champaign.

The results will be presented this week at the annual meeting of the American Educational Research Association and will be detailed in the May issue of the journal Phi Delta Kappan.

"These results call into question common assumptions about public and private school effects, and highlight the importance of carefully considering socioeconomic differences in comparisons of school achievement," write Lubienski and her husband and co-author, Christopher Lubienski.

The data was pulled from the 2000 National Assessment of Educational Progress (NAEP), the most recent annual assessment whose raw data is available for review. The students in the study included more than 13,000 fourth-graders in 607 schools (385 public and 222 private) and more than 15,000 eighth-graders in 740 schools (383 public and 357 private).

Socioeconomic status was determined from surveys of the students regarding eligibility for free or other financial assistance, reading material in the student's home, computer and Internet access at home, and the amount of time parents spent discussing homework. Education levels of eighth-grader parents was also factored in.

The results fly in the face of assumptions used by policy makers to direct the future of education.

"All the most prominent reforms right now assume that private schools do better, and that if you take a disadvantaged kid and give that kid an option to go to a private school, that will boost their achievement," Christopher Lubienski said.