WASHINGTON — The opportunity divide that begins at birth is widening, reinforcing inequality as American children progress through school.

Kids born to middle- and lower-income families could find it harder to catch up in later life as wealthier children enjoy ever larger advantages.

Among them: Wealthy parents are spending more lavishly on childcare, education and accessories such as toys, while families in the middle are spending roughly the same or less after inflation. And extracurricular activities such as after- school clubs have increasingly become the province of privileged kids.

Such advantages sweeten the transcripts of children from wealthier homes. That could give them a head start when it comes to enrolling in college, where they already have the advantage according to a 2014 report from the Herndon, Virginia-based National Student Clearinghouse. The divergence comes at a time when a college degree is becoming a prerequisite for a middle- class living standard.

“We’ve added post-secondary education and training as the capstone to a very powerful system of inequality, and the inequality is self-reinforcing,” said Anthony Carnevale, director for the Georgetown University Center on Education and the Workforce in Washington.

A student at one of America’s most selective colleges is 14 times more likely to be from a high-income family than from a low-income one, based on a 2010 study by Carnevale and fellow Georgetown University economist Jeff Strohl. Those schools usually admit less than one-third of applicants.

For an upper-middle-class American, getting a degree is “part of your biography”, said Carnevale. “But for other kids, it has to be an aspiration.”

Khalil Johnson, 19, is the first in his family to get a post-secondary education. He’s attending Pitzer College in Claremont, California, near Los Angeles, after graduating from a Catholic school in Philadelphia that he attended on a scholarship. Getting there was challenging, at times.

Johnson borrowed a friend’s old study guide to prepare for the college entrance exam because he couldn’t afford a new one. He filled in any gaps by thumbing newer versions for free at a local bookstore. At the same time, his classmates from more affluent households were attending classes and summer camps to prepare for the test.

“I felt at a disadvantage,” he said.

Tuition is also an issue for students like Johnson, who had to forgo attending the University of Vermont because he couldn’t afford the cost — $48,654 a year in tuition, fees room and board for out-of-state students.

Nationwide, the price of education, fees, room and board at a four-year institution climbed to an average $23,872 in 2012-13 from $10,975 four decades earlier, based on National Center for Education Statistics data adjusted for inflation.

Making higher education more affordable is one of the main economic themes President Barack Obama plans to carry into his final two years in office. Last week, Obama proposed providing a free community college education as an entitlement to millions of students, a plan that will cost $60 billion over 10 years.

Family income also affects success on campus. Graduation rates for high-income students climbed to 54 percent for those born in 1979-1982, from 36 percent for those born in 1961-1964. By contrast, graduation rates for low-income students had improved by just 4 percentage points, to 9 percent, based on a December 2011 paper by University of Michigan economists Martha Bailey and Susan Dynarski.

That’s important, because graduating has almost become a prerequisite in landing better-paying jobs. A four-year degree translated to 56 percent higher average wages between 1970 and 2013, based on Federal Reserve Bank of New York research.

Bachelor’s degree holders over the age of 25 made $1,108 per week in 2013, based on Bureau of Labor Statistics data, compared with $727 for someone with some college and no degree and $651 for those with a high school diploma.

Schools’ admissions policies are contributing to the divide. Top colleges are filling more of their classes in early- entry programs that favor wealthier families, placing another barrier before poorer students.

As inequality grows, the children of less affluent families also are falling behind in spending on transcript-sweeteners that could improve their odds of getting into better schools.

Since the 1970s, wealthy students have become more active in clubs and sports, while working-class teenagers lag behind, Kaisa Snellman, an economic sociologist at global graduate business school INSEAD, wrote in a paper published in the January 2015 ANNALS of the American Academy of Political and Social Science.

Three-quarters of students born in 1986 from the top 25 percent of households participated in non-sport activities as high school seniors, compared with 55 percent of those from the bottom 25 percent. The gap between the two extremes was less than 10 percentage points for those born in 1954.

“Participation in extracurricular activities is closely correlated with children’s futures,” Snellman wrote. “Playing lacrosse or squash is indicative also of cultural capital, because it signals that a student will fit well at an elite institution.”

Upper-income families also spend far more on their kids in general, and the gap is increasing.

Outlays on childcare, education and accessories such as toys by those at the 10th percentile — who make less than the top 9 percent and more than the other 90 percent — jumped 76 percent to $11,013 in 2006-2007 from 1972, based on a study co- authored by Sabino Kornrich, a sociologist at Emory University in Atlanta. Families further down the scale saw much smaller increases, and those right at the middle spent $2,217, down 0.6 percent, adjusting for inflation.

D’Anne and Bruce McFarlane, 55 and 54, are among those who’ve leveraged high incomes to help their kids succeed. Bruce’s earnings as principal at an intellectual property consulting firm and later as founder of Litinomics, a commercial litigation consulting business, allowed D’Anne to stay home and raise their now 23-year-old son and 20-year-old daughter.

The children grew up in a house now valued at $2.4 million that’s tucked into a manicured Mountain View, California, neighborhood. Being an at-home mom allowed D’Anne to drive the kids to sports practice and keep tabs on their day-to-day activities, she said. For a year, the family even moved to Rome, which helped give the children a more global education.

“They were incredibly lucky,” D’Anne McFarlane said of her children, who are both pursuing bachelor’s degrees.

As upper-income households help their kids become more well-rounded, it’s harder for middle- and lower-income children to compete.

During her two-decade career as a guidance counselor, Ruth E. Lohmeyer has worked with affluent students and with those who ring up groceries after school to make ends meet. She’s seen socioeconomic divides spill over into academic success from her vantage point at Lincoln Northeast High School in Lincoln, Nebraska.

Middle-income and lower-income kids miss extra-curricular club meetings for after-school jobs, while upper-income students’ parents pay their cell-phone bills so they can join activities, she said. Richer families also can afford to have their teens join sport teams, visit out-of-state colleges and take lessons on how to boost achievement-test scores that will help get them into better universities, said Lohmeyer, 57.

“We want them to be more of a 3-D student, where they’re achieving academically, involved in their school, involved in community service,” she said.