Students were routinely kept in small concrete "isolation boxes" for days and weeks at a time as punishment at a private boarding school for troubled teenagers that is now under FBI investigation, former students told The Associated Press.

Six former attendees at Midwest Academy in Keokuk, Iowa, described the cell-like rooms, where they had to sit quietly on the floor in a specific posture for 24 hours in order to get out. The harshly lit rooms with small windows were often filled with the sounds of students screaming and motivational recordings piped in through speakers, they said. 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. 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," said Emily Beaman, 17, of Wheaton, Illinois.

After weeks of isolation, Beaman said, 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 Jan. 28 to investigate allegations that a staff member sexually assaulted a student. The investigation has since expanded to other possible criminal activity and abuse. Academy owner Ben Trane declined to comment on abuse claims at a news conference this month and didn't respond to AP interview requests. The academy's 90 students were removed and it's temporarily closed. Three students interviewed by the AP said they have spoken with the FBI.

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 $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 program saved teens' lives.

As a privately funded school without state-ordered placements, the academy didn't require a license to operate and was otherwise unregulated. "It flew under the radar," said Drake University professor Jerry Foxhoven, an Iowa juvenile law expert who'd never heard of the program previously.

Foxhoven said long-term isolation can be very damaging for juveniles, exacerbating mental illnesses and causing lasting effects that may include post-traumatic stress disorder. He said parents wouldn't be allowed to keep children in isolation for weeks without facing abuse allegations, and the academy shouldn't, either.

Former students said the school kept parents in the dark by strictly limiting and monitoring their communications. Only now, they say, are some of their claims being taken seriously.

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

"That is the worst I've ever been treated," said Shaun McCarthy, 19, of Avoca, Iowa, who said he was lucky to go into isolation only twice. "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. In that role, 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. No one else would clean up the bodily fluids, so it fell to him.

To get out, students said they had to sit in a certain way for 24 hours. Sometimes, lengthy essays were required.

"They use seclusion preemptively and as a punitive measure," said former student said James Farris, 24, a nursing assistant in St. Petersburg, Florida. "This is illegal in public health care settings, yet somehow they get away with it."

Farris recalled waking up in an isolation box on his 18th birthday and demanding his release, screaming when it took hours to accomplish. He said he had nightmares for years.

Rachel Adkisson, 19, of Des Moines, said she was put in isolation for refusing to run during gym and had lost 20 pounds when she left two weeks later. She said she told the FBI about another girl who tried to kill herself by tying her bra strap 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?"