IOWA CITY, Iowa — The owner of a boarding school for teenagers coerced one student into a sexual relationship, had girls undress during “body image therapy” sessions and put some students in solitary confinement for days, Iowa prosecutors alleged Friday.

Former Midwest Academy director Benjamin Trane, 39, pleaded not guilty to charges of third-degree sexual abuse, sexual exploitation by a counselor and child endangerment. A judge ordered that he be held at the Lee County Jail on a $500,000 cash-only bond.

The charges come after a 19-month investigation into alleged abuse at the private, for-profit boarding school in Keokuk, in Iowa’s southeastern corner. The school, which enrolled about 100 students from mostly well-off families across the United States, closed in January 2016 after investigators served search warrants there.

Division of Criminal Investigation special agent Joe Lestina alleged in criminal complaints that Trane abused his power to pursue sexual relationships with students while putting others at risk by keeping them in isolation.

Trane performed multiple sexual acts on one girl throughout 2015, coercing her to engage in them “in order for her to successfully participate and ‘level up’ in the program and to be able to contact her family members,” Lestina wrote.

Trane held counseling sessions that included “body image therapy” in which girls would undress and stand in front of a mirror to discuss their bodies, the complaint said. Trane engaged in sexually explicit conversations with students, made them answer written questionnaires about sex and had physical contact with some “for the purpose of sexual arousal, gratification and attempted grooming,” Lestina wrote.

Trane also enforced policies that “created a substantial risk to the students’ physical, mental or emotional health and/or safety, including but not limited to solitary confinement for extended periods of time,” he wrote. Former students have said that they were forced to stay in small concrete “isolation boxes” for days or weeks at a time.

Former student Kennedy Thayer, who was at the academy in 2015 and interviewed multiple times by investigators, said she was relieved Trane was charged and jailed.

“He might finally understand a little bit of what we went through,” said Thayer, now a 19-year-old cheerleader at Nebraska Wesleyan University. “But jail is nothing compared to that place. It was horrible.”

She recalled Trane commenting on the shape of her body, taking three of her younger classmates shopping for lingerie at Victoria’s Secret, and forcing her to answer a questionnaire about her sexual history and fantasies. Thayer said she reported some of Trane’s actions to her mother, who called to complain.

“He flipped out and said, ‘you can’t do things like that because I can make you stay longer’,” Thayer said.

Trane had been living in Idaho Falls, Idaho, since the school’s closure and told the court he’s unemployed. He’s married and has several children.

Several former students have filed a lawsuit seeking damages for their treatment from Trane, his company and Midwest Twister LLC, which is owned by Utah businessman Robert Lichfield.

Midwest Twister owned the academy’s campus, and leased it to Trane’s corporation in exchange for payments based on student enrollment. Lichfield, who has a long history of involvement in controversial boarding schools, argues his company had no control over the academy’s operations and is asking to be dismissed.

David Ferleger, the students’ attorney, said Friday’s charges back up their claims that they were abused for years in a facility that had no state oversight and charged families $5,000 per month.

“It’s a great blessing for the kids that the FBI and state police took it over and freed them from this awful abuse,” he said.