The preschool teacher walked a 4-year-old student to his apartment in Rogers Park, a neighborhood in Chicago where many straddle the poverty line. On this September evening, Cayla Calfee, 23, met the boy’s mother, a full-time nanny for two families. They discussed the boy’s goals, the application process for a competitive kindergarten.

The boy, comfortable between the women, handed his teacher a motocross toy. The toy was a casualty of play, with snapped handlebars. He was eager to share now. When class started four weeks ago at the Howard Area Community Center, he barely held eye contact.

These moments, however slight, are why Calfee keeps education theory textbooks on her coffee table. It’s why she signed up for the 12-hour workday, why her biggest splurge now is a carton of frozen yogurt.

The sacrifice of this lifestyle, she said, is a privilege. Not everyone can afford to be a preschool teacher.

Calfee graduated last year from Indiana University with a bachelor’s degree in early childhood education – the major with the lowest lifetime pay, according to a new study.

Researchers at the Brookings Institution’s Hamilton Project recently set out to answer: As student debt rises — and devours our wealth — how do the high school students of today, feverishly applying to colleges this fall, decide what they can afford to study?

A college degree, in any major, significantly increases your lifetime earning potential, the study found. Some do more than others. But all do more than Calfee’s.

The financial stakes have never been higher: About 70 percent of workers with bachelor’s degrees have some amount of student debt, said co-author Brad Hershbein, a labor economist at Upjohn Institute for Employment Research and a visiting fellow at Hamilton. The average student with debt graduates with $33,000 in loans, according to a recent analysis by Edvisors.

Calfee, who grew up in a Chicago suburb, has no debt. Her family financed her college education. Students in early childhood education at Indiana, she said, were not allowed to hold jobs during unpaid student-teaching semesters.

“I was lucky to be able to pursue my dream career,” Calfee said. “Economic barriers keep talented students out of this field. It’s hard to pay for school, housing and food on your own.”

And she was fully aware of the average annual pay after graduation: $27,000.

The Hamilton Project researchers analyzed career earnings for 80 undergraduate majors from the Census Bureau’s American Community Survey and found that, at every career stage, college graduates as a group fare better than workers whose educations didn’t continue after high school. What’s less obvious, and perhaps more useful when picking a major: Median lifetime pay for college graduates varies greatly, depending on what they studied.

Hershbein hopes high school and college students will snoop through the project’s salary database, which is being released Monday. (You can compare career earnings across majors here.)

“The intent is not to induce people to pick a certain major or deter them from another one,” Hershbein said. “Study what you like, what you’re good at — and then plan for how much money you’ll make, how you’ll be able to pay off student debt.”

One year after graduation, Calfee makes $48,000 per year, which puts her in the top 10 percent of earners in her field. She lives with her boyfriend in Evanston, Ill., pays $900 per month in rent and bikes nine miles to work each day. She’s saving to buy a car.

After reading Jonathan Kozol’s “Savage Inequalities,” which details the challenges students face in low-income areas, Calfee pledged to spend her career helping inner-city kids shape brighter futures.

“Your Zip code or the color of your skin should not determine the quality of your education,” she said.

The value of her college education should not be measured in dollar signs, Calfee said. Her coursework inspired her teaching philosophy – the same teaching philosophy she says helped the 4-boy-old boy ease out of his shell.

Calfee hopes that more scholarships become available for college students who want to study early childhood education but can’t shoulder tuition costs. The work will always be a privilege, she says. It shouldn’t, however, be restricted to the privileged.