A new report from the Pew Research Center finds that 40 percent of households with children under the age of 18 include mothers who provide the sole or primary source of income for the family.
In 1960, that figure stood at just 11 percent.
Bryce Covert, the Economic Policy Editor at ThinkProgress, said there are a couple of different factors at play in this dramatic shift. First, she said, women have entered the labor force in dramatic numbers since the 1960s. Also, women are getting much more education, which increases their earning potential.
"The other half of this trend, however, is due to a rise in single motherhood," Covert said. "The majority of these women whose families are relying on their income are actually single mothers. And that is not necessarily a story of women's economic victory."
In many cases, these women are making a lot less than other households with two earners, she said.
"When it comes to single mothers, there's a lot of economic hardship that tends to fall on them," she added "A lot of them are employed in low-wage jobs in the retail sector or the service sector that also come with very few benefits."
Covert said the U.S. support system for single parents is especially weak — "it's been rated the worst country for single parents, among many developed countries" she said — with no guarantee of paid time off when a child is born or if a child gets sick.
She says, while single-motherhood doesn't have to be difficult, that it is makes it hard to be excited about this news.
Americans aren't sure, as a group, how to feel about this shift in women earning, either.
Covert said the sentiments are changing. Two-thirds of Americans now disagree with the idea that it's better for a husband to make more than his wife, while about 40 percent felt that way 15 years ago.
"That's a huge change," Covert said. "But a lot of people feel that women's entrance into the labor force has made it harder for parents to raise children. They say it's made marriages more difficult to succeed."
Generally, Covert said, there's a lot of ambivalence toward the data among Americans. They're not looking to revert to the Leave It To Beaver era, she said, but they're also concerned about what this means for raising children and having families.