ST. LOUIS • Coming back to Washington University for their 25th year reunion felt a little odd at first for Heather Calvin and Bonnie Adrian.

Their college experience wasn’t like most people’s.

Their junior year, they sued the university.

The issue was over the ThurtenE carnival, touted as the oldest student-run carnival in the country, which was hosted on campus last week. It’s the main function of the junior honor society, ThurtenE, that up until 1991 allowed only men as members.

Title IX, a federal sex discrimination law, had been around for 20 years before the lawsuit. Among the many issues the law addresses is that social fraternities and sororities are exempt from the rules of gender-specific organizations.

An honor society, such as ThurtenE, had no such exemption, but it had continued operating as it traditionally had for decades without any challenge — until Calvin and Adrian decided to apply their junior year.

“I really earnestly thought it would be a very cool thing to be part of the carnival,” said Calvin, who works as an associate vice president at the Museum of Science in Boston. “When they declined and suggested we join the women’s group, that was just so wrong that I felt really compelled to challenge it even if it wasn’t going to benefit us, which clearly it wasn’t.”

The two women had been members of the sophomore honor society. But their junior year option of an honor society, Chimes, left them wanting more.

Within the year, both organizations would become co-ed.

But the challenge to the status quo brought a lot of negative attention to the two women, which they document in a blog that links to old newspaper stories about their case.

“I’m not sure we would have done it if we had as much perspective on how hard it was going to be,” Calvin said. “There’s a certain bravery that comes with youthful immaturity, and I think that worked to our advantage. It made us willing to take that risk in a different way. “

A local attorney took on the women’s case pro bono and worked the legal angle, while a grievance committee on campus tackled it internally. Eventually, the grievance committee decided there wasn’t enough proof that discrimination occurred when Calvin and Adrian applied to ThurtenE, but it did call for changes that led ThurtenE to start accepting female students.

The women dropped their lawsuit after they won on their issue. By that point, they were already members of the senior honor society, applying for jobs and trying to capture what was left of their chance of a normal college experience.

Adrian, now a research nurse scientist at the University of Colorado Hospital, said she still had mixed feelings toward her alma mater. She remembers feeling that way during graduation, too, describing it as “adversarial.”

Today, five of the 13 members of ThurtenE are women.

“The members of Thurtene Honorary 2017 recognize the first acceptance of women into the Honorary as an important point in our history,” the organization’s leaders said in a statement.

Calvin said it had been gratifying to see women participating over the years, even if few knew what it took to get there.

“On the other hand that’s a cemented victory — that it’s such a co-ed organization that people forget that 26 years ago it was not,” she said. “That’s a win.”