Few mothers have been as public and assertive as Ms. Seefeld. In 2010 her son, Mr. Warner, learned he had been accused of sexual assault by a fellow student at the University of North Dakota. Mr. Warner contended that the sex was consensual, but he was suspended and banned from campus for three years.

His mother leveraged the connections she had developed over years as a high school psychology and sociology teacher in Fargo, and as a union leader. She contacted the State Board of Higher Education and visited state legislators.

Hearing that the university was about to start a fund-raising drive, and thus would not want bad publicity, Ms. Seefeld said, she emailed its president about 9 p.m. one night. She wrote that she had hired a lawyer to look into suing the university, and a public relations firm to help her publicize her son’s case, she said. “Within 30 minutes I heard from the president,” she said, and he told her the case would be reviewed.

A spokesman for the university declined to comment. But university documents provided by Ms. Seefeld show that the school did review the verdict, and nullified it because of a new development: The police said that they had found inconsistencies in the accuser’s account and that some witnesses had contradicted it. They issued a warrant for her arrest on a charge of filing a false police report. (The woman left the state and has not been arrested. She did not respond to telephone messages.)

Realizing she was not alone, Ms. Seefeld helped found FACE, the advocacy group for accused students. She said the group does not want to attack women. But if the mothers do not defend their sons, she said, who will?

“I just thought it was so wrong, and I thought how could anybody let this stand,” she said of her son’s punishment. “And pretty much the most significant weapon I had was the weapon of public opinion, so that was the weapon I was wielding the hardest.”