Undergraduate tuition at BU tops $66,000. Where does all the money go?

It’s a question that has been nagging parents, professors, and students themselves since at least 1,000 graduate workers went on strike amid union negotiations on March 25.

The Service Employees International Union that represents the employees said the strike has disrupted about half of BU classes, forcing professors into a wide range of workarounds. A spokesperson for BU, on the other hand, said that less than 1 percent of university classes are not meeting and a relatively small number of breakout discussion groups have been disrupted. One dean suggested — among various recommendations — that professors consider the use of artificial intelligence to fill in for grad student workers.

All the while, BU has joined a growing cohort of pricey, private New England schools. Administrators announced last month the total cost of attendance will top $90,000 next school year.

By contrast, BU graduate assistants typically earn $27,000 to $40,000 annually for what is described as a 20-hour workweek, well below the $103,000 median household income in Greater Boston. Adjuncts grapple with the same experience: underpaid and overworked, with little stability or certainty.

It comes down to the complicated economics of higher education — where the cost of everything from labor to facilities drives tuition ever-upward, but the money does not always flow into classrooms as expected.

Yes, some of the tuition money families pay to BU has found its way to new buildings and flashy amenities, including maintenance of the lazy river at the campus fitness center and the recent construction of the “Jenga”-style data science building that glimmers over the Charles River. (Its geothermal heating and cooling system cost $305 million alone.)

But higher education finance experts point more to the soaring cost of labor, inflation, and volatile changes in enrollment. Dig deeper, they say, and the exorbitant price of college is really a symptom of a broader trend in the economy: income inequality.

Catharine Hill, managing director of education nonprofit organization Ithaka S&R and former president of Vassar College, said schools raise the sticker price of tuition as high as they can in the hopes that wealthy families and many international students will pay full freight. At those prices, students and their families have certain expectations in terms of both facilities and education.

“Colleges are competing for talented high-income students, and they want some of those things that they pay for,” Hill said. “Every time the sticker price for college hits multiples of 10s — $50,000, $70,000, now $90,000 — there’s this big discussion of what is going on.”

And those full-freight-paying students help schools pay the bills, which climbed in the pandemic-era years of 8 to 9 percent inflation. Larger universities can sometimes lean on their endowment. But just like costs for food, electricity, and everyday goods rose for households, they increased, too, for the 38,000-student campus along Commonwealth Avenue. The 14 construction projects the school has underway or recently finished — ranging from new sprinklers in the student union to solar panels all over campus — did not get cheaper, either.

In all, according to publicly available tax documents, the annual expenses at BU climbed 38 percent, from $2.06 billion in 2017 to $2.84 billion by 2022 — a pace in keeping with similar schools.

The tuition students actually pay is often not climbing as fast as the public perceives, especially for low- and middle-income families.

The average tuition price for private postsecondary education sat at $25,935 in 2017, before rising to $26,998 in 2022 — a 4 percent increase — according to trend data from the National Center for Education Statistics. But account for inflation, and tuition actually fell $300 in that time. (These metrics do not include the cost of room, board, and fees, which, at BU for instance, tops $20,000 a year.)

Only one-quarter of students at private universities today shell out full price, according to research from financial aid expert Mark Kantrowitz. At public institutions — which typically have lower tuition, especially for in-state students — that number is about 40 percent. Even high-dollar schools are offering more students financial aid.

The “net price” at BU — what students pay after subtracting scholarships and grants — declined from $29,154 in 2020 to $27,829 in 2022, even before taking inflation into account. Net price has also remained static or gone down at Tufts University, Wellesley College, and Boston College, according to data institutions provided to the Department of Education.

Financial aid, of course, has become one way that schools compete to attract admitted students, offering a sizable discount from their sticker price to lure admitted students they particularly want, said Donna Desrochers, a senior associate at the higher education consulting firm RPK.

“Offering student discounts based on financial need or other attributes is inherently an incentive to attend,” she said. “It’s now part of institutions’ budget conversations.”

Another huge piece of the puzzle: labor.

Since 1987, the academic workforce nationwide has shifted from mostly tenured and tenure-track faculty to include many nontenure-track professors, adjuncts, and graduate workers, according to a 2023 report from the American Association of University Professors. In theory, that should drive down costs, since tenured faculty enjoy the highest wages and flexibility to conduct research. But compensation still comprises between 40 and 70 percent of most institutions’ balance sheets, experts said.

Why? The swelling ranks of nonteaching employees at many universities. Between 1976 and 2018, the number of full-time administrators at US colleges has grown 164 percent, according to a study in the Review for Social Economy. For nonteaching professionals (everyone from admissions staff to academic counselors), the number has grown nearly fivefold.

There are a host of reasons for this — some of which relate directly to the widening array of services schools provide students. Many institutions expanded their mental health resources and tutoring options in response to mushrooming health concerns and educational discrepancies in the wake of COVID-19.

But that has left many instructors on the ground asking where they fit into the financial picture.

At the picket line, BU graduate workers recount being unable to afford rent and utilities, surviving on food stamps, and forgoing groceries because of meager wages. In 2023, only 15 of BU’s 4,366 graduate workers earned more than $50,000 for part-time work, according to the union.

Laurel Oberstadt-Petrik, a master’s student in theology, is struggling to afford a modest rent increase.

“Pay really hits close to home for me,” Oberstadt-Petrik said. “My rent is going up $110 a month, which is not something that I can afford, frankly.”

Pay for adjunct and other nontenure-track professors has also emerged as a sore spot.

Brian N. Duchaney, an adjunct at Bridgewater State University, began teaching at multiple state-supported institutions in 2007. But the positions rarely come with benefits, and Duchaney’s stipend has increased by only around $1,000 in the past 15 years, from around $3,800 to $5,200 for a semester-long course. He scrapes together enough to get by, but it’s a constant struggle.

Meanwhile, though higher-cost private schools such as BU have largely seen enrollment rebound after a brief pandemic dip, many public colleges are bracing for bigger declines due to a lack of applicants and declining birth rates. Still, their costs per student keep going up.

National data from the American Council of Trustees and Alumni found that at public institutions in Massachusetts, instructional costs for each student rose from $17,454 in 2019 to $18,459 in 2022 — adjusted for inflation.

“Students are frustrated as to why school costs $78,000 a year,” said Douglas Breault, another adjunct who teaches at both Bridgewater State and Babson College. “They want a receipt.”

Diti Kohli can be reached at diti.kohli@globe.com. Follow her @ditikohli_. Aidan Ryan can be reached at aidan.ryan@globe.com. Follow him @aidanfitzryan. Esha Walia can be reached at esha.walia@globe.com.