Children’s well-being depends on family stability, researchers agree. But some say marriage is not a critical factor in that stability — that cohabiting parents are just as likely to stay together long-term and provide the love and support children need. According to a new study from the Brookings Institution, that just isn’t the case: There’s no substitute for marriage.

“It is easy to see why some conclude marriage per se does not matter. But here’s the thing: marriage itself is strongly associated with family stability,” wrote Bradford Wilcox, director of the National Marriage Project at the University of Virginia, and Laurie DeRose, sociology professor at Georgetown University.

American kids born to cohabiting parents are twice as likely to see their parents break up than children born to married parents. This holds across education levels. Before children turn twelve, 41 percent of cohabiting parents with low education split up, as opposed to 26 percent of their married counterparts. The gaps are actually bigger as education increases: 45 percent of cohabiting parents with middle education break up by a child’s twelfth birthday, compared to 27 percent of married parents; among the highly educated, 49 percent of cohabiters break up, compared to only 18 percent of married parents.

The American numbers are clear, but some researchers argue that the story is different in Europe. In France and Scandinavia, Andrew Cherlin, author of The Marriage-Go-Round: The State of Marriage and the Family in America Today, argued, there “are many long-term cohabiting parents who maintain families that are little different from lasting marriages.”

But DeRose and Wilcox ran the numbers, and cohabitation is much less stable for children than marriage. The researchers examined data from 16 countries in Europe and found that kids born to cohabiting couples are about 90 percent more likely to see their parents separate by the time they turn 12, compared to children of married parents.

In France, children are 66 percent more likely to see parents break up if they are born to a cohabiting couple. This holds true for multiple education brackets: Low-educated cohabiters are more likely (23 percent) than low-educated married parents (14 percent) to break up; cohabiters of middle education (16 percent) are also more likely than married parents (11 percent) to do so, as are higher educated cohabiters (18 percent) than their married counterparts (9 percent).

The same trend holds true for Norway, where cohabiting parents are about 88 percent more likely to break up.

These results show that it is marriage, rather than education, which is most important for parents’ relationship stability. As DeRose and Wilcox wrote, “Our results suggest that there is something about marriage per se that bolsters stability.”

But why? The researchers have a few suggestions:

It could be the elaborate ritual marking the entry into marriage; the norms of commitment, fidelity, and permanence associated with the institution; the distinctive treatment of family and friends extended to married couples; or, most likely, a combination of all these things and more — that promotes greater commitment and stability.

Marriage is defined by lifelong commitment, even if that commitment is not always honored. “By contrast, the very freedom and flexibility that makes cohabitation so attractive to some adults means that cohabitation is per se less institutionalized and therefore less stable.”

“That’s why,” DeRose and Wilcox conclude, “even in highly developed and secular societies found in Europe, the institution of marriage is imbued with a stability advantage that benefits children.”

But how does it benefit kids? Interestingly, scholars argue that stable parent relationships are correlated with wise decisions. “Children who see the end of their parents’ relationship and additional partners coming in and out of the home are more likely to act up in school, end up pregnant as teenagers, and be delinquent. The damage caused by instability has been described by many scholars of all political inclinations.”

Parents need to make the decisions that work best for them, but the best thing for children, according to these results, is to have parents who are married bring them into this world.