Study after study confirms that children in married-parent families grow up to be better off financially than the children of single and divorced parents.

This makes intuitive sense, of course; a single parent supporting her kids with only one income is going to have a tougher time giving her kids the same advantages that a child of a two-parent family will get. But it's not that simple. New research confirms that income accounts for less than half of the advantage that the children of married couples get. In fact, it's married couples' parenting behaviors that have the bigger effect.

the adult children of married couples earn more than the kids of non-marrieds. parenting accounts for much more of that than income.

The Brookings Institution's Kimberly Howard and Richard Reeves recently found that children from married families were 14 percentiles ahead of other kids on the income ladder, and their parents' income accounts for only 4.5 of those 14 points. That is, children of married mothers ended up at the 57th percentile, compared to the 43rd for children of mothers who weren't continuously married. That's after controlling for other factors, like education — people with bachelor's degrees both earn more and are more likely to get married these days, for example.

However, parenting behaviors, like time spent reading to kids, account for a much larger share of the gap — 7.5 percentiles, to be exact.

There is a common-sense reason to why this bump is so great. A pair of mediocre married parents will have way more time to spend with their kids than even an exceptionally devoted single dad — someone has to do the laundry, after all, and only one of these families has a spare parent around to read to the kids while the other cleans the clothes.

even the best single dad won't have as much time to spend with the kids as a married couple

The question that continues to loom, of course, is what to do with this information. Former White House Press Secretary Ari Fleischer earlier this year advocated promoting marriage prior to childbearing as a solution to inequality in a controversial Wall Street Journal op ed.

That upset a lot of people, but it's true that here and now, marriages are more likely to be stable, committed relationships than cohabiting relationships, as Brookings' Isabel Sawhill argues in a new book, Generation Unbound. In one 2007 study she cites, only around 52 percent of women who were cohabiting when they gave birth were with their partners five years later, compared to 80 percent of married women.

But of course, it's not the wedding ring that magically makes a couple stable and baby-ready. And more importantly, it's remarkably hard to promote marriage, as the federal government has found with its unsuccessful marriage promotion initiatives. Whatever the causes for the decline of marriage, that tide will be tough to turn back, so Sawhill says it's time to help people take charge of and plan their own child-bearing.

"The old social norm was, 'Don't have a child outside of marriage.' The new norm needs to be, 'Don't have a child until you and your partner are ready to be parents,'" as Sawhill wrote at the New York Times this weekend.

If the federal government is truly interested in using social policy to reduce inequality, then, it is likely more effective to help people choose when to have children, rather than hoping they marry before they do.