STANFORD (US)—Children being raised by same-sex couples have nearly the same educational achievement as children raised by married heterosexual couples, according to a new study that used data from the 2000 U.S. Census.

“The census data show that having parents who are the same gender is not in itself any disadvantage to children,” says Michael Rosenfeld, associate professor of sociology at Stanford University.

“Parents’ income and education are the biggest indicators of a child’s success. Family structure is a minor determinant.”

Details appear in the journal Demography.

The findings show that about 9.5 percent of children living with adults identifying themselves as same-sex partners repeated a grade, compared with nearly 7 percent of children raised by heterosexual married couples who were held back a year.

The difference between the groups pretty much vanishes when taking into account that the heterosexual couples were slightly more educated and wealthier than most gay parents, Rosenfeld says.

The findings have been cited by lawyers fighting Proposition 8, the gay marriage ban passed by California voters in 2008. A federal court judge recently overturned the ban, and the ruling is under appeal.

Children of gay and married couples had lower grade-repetition rates than their peers raised by opposite-sex unmarried couples and single parents. And all children living in some type of family environment did much better than those living in group housing.

Children awaiting adoption or placement in a foster home were held back about 34 percent of the time.

“One of the fundamental issues in modern family law that differs from state to state is whether same-sex couples can adopt,” Rosenfeld says.

“My research makes clear that there’s a huge advantage to kids to be out of the care of the state and into the care of any family, even if the family is not perfectly optimal.”

Educators, policymakers and social scientists have long known that children left back in school are at greater risk than their peers for not finishing high school and getting into trouble.

Because gays and lesbians make up such a tiny sliver of the American population—only 1 percent—it has been difficult for researchers to conduct a representative study of how their children perform in the classroom. And gay marriage opponents have criticized earlier studies for having sample sizes that are too small.

“Sample size is power,” Rosenfeld says. “And the census is the biggest sample we have. This study is based on a sample of thousands and thousands of kids.”

Rosenfeld acknowledges his research isn’t going to change the minds of most people opposed to same-sex unions, but says the new data should debunk assertions—whether based on a lack of knowledge or some unfounded fear—that children raised by gay couples cannot thrive.

“Social scientists have an obligation to shed light where they can on issues that are roiling the public,” he says.

“Sometimes we have to throw up our hands and admit that something is unknowable. But in this case, we could bring some real hard data to bear on an area that was otherwise really in the dark.”

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