A boarding school for troubled teenagers in Iowa that is being investigated by the FBI routinely kept pupils in small concrete “isolation boxes” for days or weeks and wouldn’t let them

out unless they sat in a specific posture for 24 hours, according to several former students.

Six former students recently described the abuse they say they suffered while attending Midwest Academy in Keokuk, a city along the Mississippi River where Iowa borders Illinois and Missouri.

They said the dark, cell-like punishment rooms were often filled with the sounds of students’ screams and motivational recordings piped in through speakers. Surveillance cameras and staff members kept watch.

“You spend your time pounding your head against the wall. You can’t sleep because there is a lot of noise,” said Emily Beaman, 17, of Wheaton, Illinois. “A lot of girls like to scream in there. You basically look forward to bathroom breaks and those moments when you can get out of your box.”

Beaman said that after weeks of isolation, she got out in July only after cutting herself with a bottle cap and begging emergency responders to place her elsewhere. She said an earlier escape attempt failed.

The students, who attended the academy between 2008 and last September, said they and their classmates mutilated themselves, hated the lack of activity and natural light, and lost weight due to small meals. Some said they were scarred by the experience months or years later.

Officers raided the academy on January 28 to investigate allegations that a staff member sexually assaulted a student. The investigation has since expanded to other possible criminal activity and abuse. The academy’s 90 students were removed and it has been temporarily closed.

Lauren Snyder, 17, of Springfield, Missouri, recalled begging to get out of isolation last year, after an employee turned up the audio recordings so loud that the speakers blew out and were making a screeching noise.

“It was complete hell,” she said.

Snyder said she eventually attempted suicide by tying a sock around her neck, and was sent to a psychiatric hospital the next day.

After being placed in isolation her first day for refusing to take out a belly button ring, Sarah Wilson said she made a point not to return.

“I knew I would lose my mind in there,” said Wilson, 20, of Rock Island, Illinois.

The academy says it provides “struggling teens with a safe, structured and disciplined environment”.

Many middle- and upper-class families from Midwest states and beyond sent misbehaving teenagers to the academy, which costs roughly US$5,000 per month. Trane has said the students were fortunate to have its staff in their lives. Other supporters include parents who say the programme saved teens’ lives. As a privately funded school, the academy didn’t require a licence to operate.

A typical academy day started with physical education, followed by hours of school work and meetings. Former students said the goal for many was to avoid an “out-of-school suspension” for violating rules, recalling fighting and insubordination were some reasons they were put in isolation.

“That is the worst I’ve ever been treated,” said Shaun McCarthy, 19. “It’s not humane.”

McCarthy complained about the small meals and lack of stimulation, but said it was worse for others. Students who reach “level 3” in the academy’s points-based advancement system help staff watch the boxes.

McCarthy said he saw one girl puncture her finger, draw on the walls with her blood and go to the bathroom on the room’s floor before staff intervened. To get out, students said they had to sit in a certain way for 24 hours. Sometimes, lengthy essays were required.

Rachel Adkisson, 19, said she was put in isolation for refusing to run during gym and had lost 9kg when she left two weeks later. She said she told the FBI about another girl who tried to kill herself by tying her bra around her neck.

“It’s like torture,” Adkisson said. “You think it’s never going to end. You think, how can a human do this to another person?”