KAY HYMOWITZ IN THE NEW YORK TIMES: How Single Motherhood Hurts Kids.

The sociologist Kathryn Edin has shown that unlike their more educated peers, these younger, low-income women tend to stop using contraception several weeks or months after starting a sexual relationship. The pregnancy — not lasting affection and mutual decision-making — that often follows is the impetus for announcing that they are a couple. Unsurprisingly, by the time the thrill of sleepless nights and colicky days has worn off, two relative strangers who have drifted into becoming parents together notice they’re just not that into each other. Hence, the high breakup rates among low-income couples: Only a third of unmarried parents are still together by the time their children reach age 5.

Also complicating low-income single parenthood in America is what the experts call “multipartner fertility.” Both divorced and never-married Americans are more likely to repartner and start “second families” than Europeans, but the trend is far more common among unmarried parents. According to data from the Fragile Families and Child Wellbeing Study at Princeton and Columbia Universities, over 60 percent of low-income babies will have at least one half sibling when they are born; by the time they are 5, the proportion will have climbed to over 70 percent.

All of this would be of merely passing interest if it weren’t for the evidence that this kind of domestic churn is really bad news for kids. The more “transitions” experienced by a child — the arrival of a stepparent, a parental boyfriend or girlfriend, or a step- or half sibling — the more children are likely to have either emotional or academic problems, or both. (My own research indicates that boys, especially, suffer from these transitions.)

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