ANN ARBOR, Mich. >> Jessica Schairer has so much in common with her boss, Chris Faulkner, that a visitor to the day care center they run might get them confused.

They are both friendly white women from modest Midwestern backgrounds who left for college with conventional hopes of marriage, motherhood and career. They both have children in elementary school. They pass their days in similar ways: juggling toddlers, coaching teachers and swapping small secrets that mark them as friends. While Faulkner, as the boss, earns more money, the difference is a gap, not a chasm.

But a friendship that evokes parity by day becomes a study of inequality at night and a testament to the way family structure deepens class divides. Faulkner is married and living on two paychecks, while Schairer is raising her children by herself. That gives the Faulkner family a profound advantage in income and nurturing time, and makes their children statistically more likely to finish college, find good jobs and form stable marriages.

Faulkner goes home to a trim subdivision and weekends crowded with children’s events. Schairer’s rent consumes more than half her income, and she scrapes by on food stamps.

“I see Chris’ kids — they’re in swimming and karate and baseball and Boy Scouts, and it seems like it’s always her or her husband who’s able to make it there,” Schairer said. “That’s something I wish I could do for my kids. But number one, that stuff costs a lot of money and, two, I just don’t have the time.”

The economic storms of recent years have raised concerns about growing inequality and questions about a core national faith, that even Americans of humble backgrounds have a good chance of getting ahead. Most of the discussion has focused on labor market forces like falling blue-collar wages and lavish Wall Street pay.

But striking changes in family structure have also broadened income gaps and posed new barriers to upward mobility. College-educated Americans like the Faulkners are increasingly likely to marry one another, compounding their growing advantages in pay. Less-educated women like Schairer, who left college without finishing her degree, are growing less likely to marry at all, raising children on pinched paychecks that come in ones, not twos.

Estimates vary widely, but scholars have said that changes in marriage patterns — as opposed to changes in individual earnings — may account for as much as 40 percent of the growth in certain measures of inequality. Long a nation of economic extremes, the United States is also becoming a society of family haves and family have-nots, with marriage and its rewards ever more confined to the fortunate classes.

“It is the privileged Americans who are marrying, and marrying helps them stay privileged,” said Andrew Cherlin, a sociologist at Johns Hopkins University.

About 41 percent of births in the U.S. occur outside marriage, up sharply from 17 percent three decades ago. But equally sharp are the educational divides, according to an analysis by Child Trends, a Washington research group. Less than 10 percent of the births to college-educated women occur outside marriage, while for women with high school degrees or less the figure is nearly 60 percent.

Long concentrated among minorities, motherhood outside marriage now varies by class about as much as it does by race. It is growing fastest in the lower reaches of the white middle class — among women like Schairer who have some postsecondary schooling but no four-year degree.

Schairer’s life offers a vivid example of how rapidly norms have changed. She grew up in a small town outside Ann Arbor, where her life revolved around church and school and everyone she knew was married.

“I thought, ‘I’ll meet someone, and we’ll marry and have kids and the house and the white picket fence,”’ she said. “That’s what I wanted. That’s what I still want.”

She got pregnant during her first year of college, left school and stayed in a troubled relationship that left her with three children when it finally collapsed six years ago. She has had little contact with the children’s father and receives no child support.

With an annual income of just under $25,000, Schairer barely lifts her children out of poverty, but she is not one to complain. “I’m in this position because of decisions I made,” she said.

She buys generic cereal at about half the brand-name price, takes the children to church every week and posts their happy moments on her Facebook page. Inequality is a word she rarely uses, though her family life is a showcase of its broadening reach.

“Two incomes would certainly help with the bills,” she said. “But it’s parenting, too. I wish I could say, ‘Call your dad.”’

PATH TO SINGLE MOTHERHOOD

Although she grew up in the 1990s, Schairer’s small-town childhood had a 1950s feel. Her father drove a beer truck, her mother served as church trustee and her grandparents lived next door.

Her first thought when she got pregnant in college was “My mother’s going to kill me.” Abortion crossed her mind, but her boyfriend said they should start a family. They agreed that marriage should wait until they could afford a big reception and a long gown.

Schairer has trouble explaining, even to herself, why she stayed so long with a man who she said earned little, berated her often and did no parenting. She was 25 when the breakup made it official: She was raising three children on her own.

She had just answered an ad from a child care center that needed a teacher’s assistant. Faulkner hired her and promoted her twice, most recently to assistant director.

“She was always stepping out of the classroom and helping,” Faulkner said. “She just had that drive, that leader in her. I trust her completely.”

A BROADENING GAP

Despite the egalitarian trappings of her youth, Schairer was born (in 1981) as a tidal surge of inequality was remaking American life. Incomes at the top soared, progress in the middle stalled and the paychecks of the poor fell sharply.

Four decades ago, households with children at the 90th percentile of incomes received five times as much as those at the 10th percentile, according to Bruce Western and Tracey Shollenberger of the Harvard sociology department. Now they have 10 times as much. The gaps have widened even more higher up the income scale.

The reasons are manifold: the growing premium a college education commands, technological change that favors mind over muscle, the growth of the financial sector, the loss of manufacturing jobs to automation and foreign competitors, and the decline of labor unions.

But marriage also shapes the story in complex ways. Economic woes speed marital decline, as women see fewer “marriageable men.” The opposite also holds true: Marital decline compounds economic woes, since it leaves the needy to struggle alone.

That is the essence is the story of Faulkner and Schairer. What most separates them is not the impact of globalization on their wages but a 6-foot-8-inch man named Kevin.

SCHOOL TRIPS AND SCOUTING

Kevin Faulkner works the sunrise shift twice a week, leaving home at 5:30 a.m. for a computer programming job so he can leave work in time to take his sons to afternoon swim practice. Jeremy, 12, is serious and quiet. Justin, 10, is less driven but more openly affectionate. The couple’s life together has unfolded in to-do-list style. They did not inherit wealth or connections or rise on rare talent. They just did standard things in standard order: high school, college, job, marriage and children. “I don’t think I could have done it any more by the books,” Chris Faulkner said.

The secret to their success resides in part in old-fashioned math: strength in numbers. Together, the Faulkners earn nearly three times as much as what Chris Faulkner earns alone. Their high five-figure income ranks them near the 75th percentile — hardly rich, but better off than nearly 3 of 4 families with children.

For Schairer, the logic works in reverse. Her individual income of $24,500 puts her at the 49th percentile among parents: smack in the middle. But with only one paycheck, her family income falls to the 19th percentile, lagging more than 4 out of 5.

The Faulkners built a house in Livingston County because of the good schools. Schairer cares about education, too. But with Ann Arbor rents wreaking havoc on her budget, she is considering a move to a neighboring town where the school system lags. She shops at discount grocery stores and tells daughter Savannah, 7, to keep away a friend who raids the cabinets.

“I feel bad, like maybe she’s not getting enough to eat,” Schairer said. “But sometimes I don’t know what I’m going to feed my own kids, never mind another.”

Jeremy Faulkner plays tennis and takes karate. Justin plays soccer and baseball. They both swim and participate in Boy Scouts, including a weeklong summer camp that brings the annual activities bill to about $3,500.

Schairer tells an opposite story: Constraints in time and money limit her children to one sports season a year. That compounds the isolation of her 10-year-old son Steavon, who has Asperger syndrome, she said, and reduces her chances to network on his behalf. When she invited his classmates to a park on his birthday a few months ago, no one came.

“He cried and cried and cried,” she said. “I tried the parents I had numbers for, but they didn’t respond.”

While many studies have found that children of single parents are more likely to grow up poor, less is known about their chances of advancement as adults. But there are suggestions that the absence of a father in the house makes it harder for children to climb the economic ladder.

Scott Winship of the Brookings Institution examined the class trajectories of 2,400 Americans now in their mid-20s. Among those raised in the poorest third as teenagers, 58 percent living with two parents moved up to a higher level as adults, compared with just 44 percent of those with an absent parent.

A parallel story played out at the top: Just 15 percent of teenagers living with two parents fell to the bottom third, compared with 27 percent of teenagers without both parents.

“You’re more likely to rise out of the bottom if you live with two parents, and you’re less likely to fall out of the top,” Winship said.

END OF THE DAY

Left to do the showing up alone, Schairer makes big efforts. She rarely misses a weekend of church with the children, and she sacrificed a day’s pay this spring to chaperone field day at Steavon and Savannah’s school. “They were both saying, ‘This is my mom, my mom is here!”’ she said.

In February, she received $7,000 of refundable tax credits, the low-wage worker’s annual bonus. She prepaid her rent for six months and bought plane tickets to Orlando, Fla. After years of seeing pictures of Chris Faulkner’s vacations, she wanted to give her children one of their own.

They stayed with Schairer’s brother, visited SeaWorld and Gatorland, and brought back happy memories. But the trip soon began to seem long ago, more a break from their life than an embodiment of it.

Schairer sank into the couch on a recent Friday night, looking weary, and half-watched a rerun of “Friends.” Steavon retreated to his room to watch “Superman” alone, and Savannah went out to play. Kirsten, 11, was in her pajamas at 7 o’clock. They had few weekend plans.

Thirty miles away, Troop 395 was pitching tents beside a rural airstrip, where the next day the boys would take glider rides and earn aviation badges. The fields and barns looked as tidy as cartoons, and an extravagant sunset painted them pomegranate.

The clipboard in Justin Faulkner’s hands called for an early reveille.

“I’m the patrol leader,” he said, beaming.

© 2012 The New York Times Company