Eleanor Roosevelt never wanted to be first lady. For her husband, of course, she was “glad” that he was elected president of the United States in 1932. But for herself, not so much.

She knew that when she moved into the White House in a few months she would have to give up her teaching job. “I’ve liked teaching more than anything else I’ve ever done,” she told an Associated Press reporter. “But it’s got to go,” she added, a decision she hated making.

Almost nine decades later, Jill Biden, also a teacher preparing for her life in the White House, has indicated she will make a very different choice.

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Come January, when her husband’s job title changes, hers will stay the same: Unlike every other first lady in American history, she has said she will keep her full-time job.

“I’m going to continue to teach,” she said in an interview on “CBS Sunday Morning” in August. “It’s important — I want people to value teachers.”

That Dr. Biden’s career ambitions, beyond the formal duties of a first lady, are of note is a telling sign of how unrepresentative first families have become, a far cry from the reality of many American families.

Since at least the late 1950s, presidential families — at least while occupying the White House — have reflected the old-school nuclear family of the “Leave It to Beaver” sitcom variety: a heterosexual couple, married, with children; husband in the public sphere, bringing home an income; a perfectly coifed mother in the domestic sphere, managing everything from meal planning to Christmas decorations.

Through the ’50s and ’60s, this model mirrored a majority of American households and reflected the country’s broad attitudes at the time toward marriage, class and traditional gender roles.

But in the 1970s and ’80s, a combination of the women’s movement and declining wages made single-income households both impractical and undesirable.

“You had the beginnings of the unraveling of the economic prosperity of the 1950s, and it became harder and harder to get that American dream,” said Stephanie Coontz, social historian at Evergreen State College in Olympia, Wash. “Many women were joining the work force, some of them because they felt so trapped at home by this monolithic idea of what a good family is, and some because they had to.”

Except the first ladies. Even those who had carved out their own careers and identities before their husbands were elected president had to contort themselves to fit into a vintage first lady mold.

The ‘folksy’ first lady

“The title ‘first lady’ is a social title. It’s simply about being the first lady of society,” said Lisa Kathleen Graddy, curator of the National Museum of American History’s first ladies collections. The role came about in the 19th century when the White House needed a hostess to entertain guests, Ms. Graddy explained, and back then, that wasn’t necessarily the job of the president’s wife. The hostess role was more frequently occupied by other people, like daughters, daughters-in-law, or, in the case of President James Buchanan, the only American president never to marry, his young niece.