Adapted from a story by The Washington Post’s Heather Long.

According to new research from several European economists, children raised by same-sex couples had higher test scores in elementary and secondary school and were about 7 percent more likely to graduate from high school than children raised by different-sex couples.

The study by economists Deni Mazrekaj, Kristof de Witte and Sofie Cabus of Belgian university KU Leuven used government data tracking all children born in the Netherlands since 1995. The Netherlands was the first country in the world to legalize same-sex marriage in 2001 and has generally been one of the most supportive nations for same-sex couples.

“The results indicate that children from same-sex couples outperform children from different-sex couples on standardized test scores at the end of primary education by 0.18 standard deviations," the researchers wrote in their paper.

What’s unique about this latest research is that it follows all children born in the Netherlands from 1995 to 2005 through primary school (and beyond). The data includes information about the child’s educational performance as well as data on the child’s parents and family income. Prior studies of the children of gay and lesbian parents have often had a small sample size, of only a few dozen kids, or have used U.S. Census Bureau data, which is only a one-time snapshot.

In total, this latest study tracked 1,200 children raised by same-sex couples and more than 1 million kids raised by different-sex couples.

The researchers found that same-sex parents are often wealthier, older and more educated than the typical different-sex couple. Same-sex couples often have to use expensive fertility treatments to have a child, meaning they are very motivated to become parents and tend to have a high level of wealth. This is likely to be a key reason their children perform well in school, the economists found.

“It is difficult for same-sex couples to obtain children so they have to have a high socioeconomic status," said Mazrekaj, who presented the research at the American Economic Association conference in Atlanta in January.

When the economists controlled for income and wealth, there were a much smaller gap between the test scores of children of same-sex parents and children different-sex parents, although children of homosexual couples still had slightly higher scores.

Most prior studies have found no statistical difference in the educational performance or well-being of children from gay or lesbian couples (a few have found negative effects), but this latest research was also able to control for the effects of divorce, which often has a negative impact on school performance and can skew results.

“Many children come into a same-sex family through divorce of a homosexual parent with a heterosexual partner and therefore did not grow up in a same-sex family,” the economists wrote. “Divorce may exert an independent negative effect on school outcomes.”