WASHINGTON — Aljanal Carroll never doubted her ability to beat the odds — not when a doctor told her she would never attend school after battling spinal meningitis as a child, or when she set her sights on a 4.0 G.P.A. in her master’s program, or when she heard it was rare for Black women to earn a doctorate in business administration.

Then she enrolled at Walden University.

Ms. Carroll started taking classes at Walden, an online, for-profit school, in the fall of 2017, drawn by the promise that she could complete her doctoral degree in 18 months. She sailed through her coursework, but when it came time for her “capstone project” — essentially a dissertation — she hit a wall. Her review committee would take weeks to deliver feedback that amounted to little more than minor grammatical and formatting suggestions yet required her to make revisions, starting the weekslong wait all over again.

By the time Ms. Carroll’s project was approved, it was three years and tens of thousands of dollars in unexpected tuition costs later.

“It started to make me feel like I couldn’t write or speak, which didn’t make sense because I’d just earned a 4.0 for my master’s,” Ms. Carroll, 49, said. “I knew it didn’t seem right, but I was so far in it, I couldn’t turn back.”

Her experience reflects what a class-action lawsuit alleges was an insidious scheme by Walden to lure and then trap students, especially those who were Black and female, in a cycle of debt and despair. The National Student Legal Defense Network, which filed the suit in January on behalf of former students, claims that Walden violated not only consumer protection laws, but also Title VI of the Civil Rights Act by preying on minorities and women and misrepresenting the costs and credits required for getting an advanced degree.

The lawsuit, filed in federal court in Maryland, charges that Walden intentionally stretched out the process of completing a capstone project, requiring students to re-enroll for semesters on end, paying tuition all the while, while they waited for approval from a three-member committee. As a result, the suit estimates, the school overcharged students by more than $28.5 million.

“Walden lured in students with the promise of an affordable degree, then strung them along to increase profits,” said Aaron Ament, the president of the National Student Legal Defense Network. “As if that’s not bad enough, Walden specifically targeted Black students and women for this predatory program, masking its discrimination as a focus on diversity.”

The lawsuit further claims that the school engaged in “reverse redlining,” a practice usually associated with housing discrimination, by targeting minority communities with its advertising and tailoring it to appeal to women.

Walden, which has faced similar lawsuits in the past, has denied any wrongdoing. Its mission, it says, is to serve a diverse community, and the school says it has succeeded in that mission. In a motion to dismiss the lawsuit, it said that in 2020, it awarded doctorate degrees to a greater number of Black and female students than any other school in the United States.

In the court filing, the university said the suit was a “baseless and inflammatory attempt to repackage Walden’s school mission into calculated discrimination.”

In response to questions about the lawsuit, a spokeswoman for Walden said it would “continue to work to ensure that those groups of people that have been typically underrepresented in higher education know that attaining an education and expanding their access to opportunities is possible at Walden University.”

The claim that Walden violated students’ civil rights is an unusual strategy for proving predatory practices. Critics of the for-profit college sector have often denounced its tactics as impinging on civil rights when pressing for administrative or policy changes, but Title VI and reverse-redlining claims are notoriously difficult to prove in court, in part because of the need to prove intent.

Eileen Connor, the director of Harvard’s Project on Predatory Student Lending, which has pursued one of the only other lawsuits to make Title VI claims on behalf of students at for-profit colleges and universities, said courts were “suspicious of, if not hostile to, these reverse-redlining claims.”

“It’s not that the claims don’t have merit or are not worth bringing,” she said. “But to stop relentless targeting of people of color by predatory schools, it’s going to require greater involvement from regulators like the Department of Education and the Federal Trade Commission.”

Still, some experts and observers say the lawsuit against Walden could provide a road map for holding for-profit institutions responsible for targeting vulnerable populations.

“We know that there are organizations that rely on systemic racism to turn a buck, and for-profits are a part of that,” said Dominique J. Baker, an assistant professor of education policy at Southern Methodist University. “It may potentially be an opening salvo where this work is done for other institutions, or some inspiration for the Department of Education and Congress to think about ways to hold institutions accountable for their actions.”

The lawsuit highlights the unique vulnerabilities of Black female students, who disproportionately enroll in for-profit schools and who hold the most undergraduate and graduate federal student loan debt of any demographic.

Black women are increasingly becoming the face of the student debt crisis, as advocates raise pressure on the Biden administration to wipe out all $1.7 trillion in federal student loan debt.

A brief released on Thursday by the Education Trust, a think tank that supports wholesale debt cancellation, highlighted the specific plight of Black women. It detailed how they are disproportionately burdened by high college costs, a lack of wealth and obligations like parenthood that fuel their aspirations to attend college but also hinder their ability to pay for it.

Tressie McMillan Cottom, a professor at the University of North Carolina at Chapel Hill and a former for-profit college recruiter who exposed the sector’s tactics in a book, said that such schools had been able to skirt claims that they seek out students based on race and gender by using identifiers such as “underemployed, aspirational and poorly served by existing institutions.”

But Black women, she said, are especially likely to fall prey to the schools based on what they are offering.

“Black women are socialized and conditioned to pursue every kind of formal credential possible,” she said, “because they are the best way to overcome implicit bias in the labor market — and you could sell that at just about any price.”

In the motion to dismiss the lawsuit, Walden said the suit failed to prove that the capstone phase of its program intentionally discriminated against Black doctoral students, or that the capstone experience was different for Black and female students than it was for any other demographic. The school called the reverse-redlining claim “novel,” adding that “seeking to educate diverse communities does not equate to racial animus.”

Walden also said that over the time that the plaintiffs attended the program, the school changed certain aspects of it, including the cost of credits, and added a disclaimer that doctorate completion times could vary.

Tiffany Fair, a lead plaintiff who was pursuing a doctorate of business administration, said she was only able to finish the program “because the university was tired of me complaining.”

“It was an absolute nightmare,” she said. “I don’t even know if anyone read my dissertation, honestly.”

Ms. Fair, who identifies as biracial and was her family’s sole breadwinner when she enrolled at Walden in 2016, said she was told that she could complete her degree in two and a half years and that with a military discount and a scholarship, she would pay a little more than $26,200.

In the end, she owed $89,000 in loans that covered what became a four-and-a-half-year endeavor. By the time she graduated in January 2021, she had completed 15 courses and 49 capstone credits — 10 more classes and 30 more credits than she had been told she would need. Her project was approved with virtually no changes, she said.

Now, Ms. Fair, 43, has a nearly $800-a-month student loan payment, which she called “crippling.”

“I feel accomplished because I worked hard,” she said. “But I’m ashamed, actually, to be part of a program that’s so predatory, and I will never get the time back that was stolen from me and my children.”

In October 2020, Ms. Carroll, another lead plaintiff, got what she wanted: to move up the ranks of her predominantly white company, where she serves as a controller. “I can stick my chest out just a little bit more, maybe be seen for all the extra hours I work,” she said.

But her voice cracked when she recalled how she had gotten there — by paying nearly $15,000 more in tuition than she had anticipated. At one point, she said, she had broken down, “hollering, crying and saying ‘I’m tired, I have two kids in college, I’ve given you everything’” to the chair of her capstone committee.

“I did not quit because of my kids,” she said. “I didn’t want them to see that ‘if Mama didn’t make it, then I can’t make it.’ To have this type of degree and all of the accolades behind it, I’m teaching my daughter that you can do anything, regardless of what’s said, what statistics are out there for us.”