Sheryl Sandberg, chief operating officer of Facebook, last year. (Scott Olson/Getty Images)

Sheryl Sandberg, the chief operating officer of Facebook, would be the first to acknowledge that she is the world’s least-typical single mom. But on this, her second Mother’s Day in that unexpected status — Sandberg’s husband, Dave Goldberg, died suddenly last May, at age 47 — she is using her Facebook platform, and that tragedy, to reassess and highlight the challenges of single parenthood.

Sandberg’s “Lean In,” her guide to women navigating a male-dominated workplace and balancing the demands of work and family, brightly proclaimed the importance of choosing well in one’s spouse. Picking the right partner, she wrote, is “the single most important career decision that a woman makes.”

Sandberg described how Goldberg, at the time of his death chief executive of SurveyMonkey, pressed her to ask for a parking space near her office at Google when she was hugely pregnant, and later insisted that she could — she had to — negotiate compensation with Facebook founder Mark Zuckerberg despite fears of alienating her would-be boss.

Now, just over a year since Goldberg’s death, Sandberg has written a Facebook post confessing error. “Some people felt that I did not spend enough time writing about the difficulties women face when they have an unsupportive partner or no partner at all,” she writes. “They were right.”

Single parenthood “is still a new and unfamiliar world,” Sandberg acknowledges. “Before, I did not quite get it. I did not really get how hard it is to succeed at work when you are overwhelmed at home.”

Well, duh, you might say, and Sandberg understands how you might have that exasperated reaction. Her story is heartbreaking, yet in her case the loss has been cushioned by the combination of an overflowing bank account and a devoted network of family and friends.

But this is precisely Sandberg’s goal: to leverage her atypical platform to bring heightened attention and understanding to hurdles faced by single mothers lacking her resources.

“I will never experience and understand all of the challenges most single moms face, but I understand a lot more than I did a year ago,” she writes. “Our widespread cultural assumption that every child lives with a two-parent heterosexual married couple is out of date. Since the early 1970s, the number of single mothers in the United States has nearly doubled. Today, almost 30 percent of families with children are headed by a single parent, and 84 percent of those are led by a single mother. And yet our attitudes and our policies do not reflect this shift.”

These societal failings have both an emotional and financial component. Sandberg and her two young children have experienced the former — the psychic injury, as piercing as it is unintended, of activities such as the father- daughter dance.

But the more intractable problem may be the financial impact of single motherhood, which is what makes Sandberg both an unlikely and an important spokeswoman.

“I realize how extremely fortunate I am not to face the financial burdens so many single mothers and widows face,” Sandberg notes. She ticks off the sobering statistics: 40 percent of families headed by a single mother live in poverty, compared with just 22 percent of families headed by a single father and 8 percent of married-couple families. For single mothers, policies such as paid leave or a higher minimum wage can be especially important.

Too often, the conversation about motherhood in the United States, in particular working motherhood, proceeds on parallel economic tracks. One, occupied by the sort of women with a copy of “Lean In” on their nightstands, seems reserved for those with the economic freedom to fret over how to balance work and family. The other is populated by those for whom the notion of “leaning in” is an imperative, not an option; theirs is an essential, perhaps the only, paycheck to support their family.

Too often, as well, the conversation about single mothers has veered between dismissing them as self-indulgent (think Dan Quayle criticizing television character Murphy Brown) and disdaining them as irresponsible.

It is possible to believe that children do best raised in a household with two married parents, as the Brookings Institution’s Isabel Sawhill has argued, and also to recognize that society has failed to adapt to the fading prevalence of this traditional model.

“There’s a lot of blame and there’s a lot of ignoring of single mothers,” Sandberg told me in a phone conversation about her post. She never expected to be among their ranks, but hers is an important voice on their behalf.

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