District Judge G. Todd Baugh sparked a furor when he said, while effectively sentencing Stacey Rambold to 30 days in jail Monday, that Cherice Moralez of Billings was "older than her chronological age" and was "as much in control of the situation" as the 54-year-old former high school teacher.
The judge's remark spawned a movement calling for him to at least be censured, and organizers say they will hold a rally Thursday.
Moralez killed herself weeks before her 17th birthday.
"I don't know what I was thinking or trying to say," Baugh told The Billings Gazette while issuing his apology Wednesday. "It was just stupid and wrong."
Rambold, who taught at Senior High School in Billings, was given a 15-year prison term, but all but 31 days was suspended and he was given credit for a day he spent behind bars, reducing the effective sentence to 30 days, the Gazette said.
Rambold pleaded guilty in April to one count of sexual intercourse without consent. The affair was discovered in 2008, but the legal proceedings were delayed by a plea agreement that required him to complete a treatment program, one he was expelled from.
During sentencing, her mother, Auliea Hanlon, testified she believed the relationship with Rambold helped drive her daughter to suicide and asked the judge to imprison him.
After the sentencing, Hanlon yelled "You people suck" and left the courtroom as Rambold was being handcuffed.
Hanlon said in a statement Tuesday Baugh's remarks at sentencing left her dumbstruck.
"She wasn't even old enough to get a driver's license. But Judge Baugh, who never met our daughter, justified the paltry sentence saying she was older than her chronological age," she said.
"I guess somehow it makes a rape more acceptable if you blame the victim, even if she was only 14."
Marian Bradley of the Montana National Organization for Women was among those calling for Baugh to be sanctioned.
"Something is not right with our system when a judge can make that kind of decision," Bradley said. "Unless we show our outrage, none of our children are safe and no one will think of us."
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend