"It's an awful thing, solitary," John McCain wrote of his time as a prisoner of war. "It crushes your spirit and weakens your resistance more effectively than any other form of mistreatment."

The United States is a leading practitioner of this "awful thing," with thousands of prisoners confined to cells, cut off from nearly all human contact, for weeks, months, even years.

The advent in recent decades of the supermax facility, oxymoronically designed for mass solitary confinement, has resulted in about 25,000 prisoners held in such conditions. Tens of thousands more are kept in restrictive segregation units at regular facilities.

The dehumanizing impact of this treatment has long been known. In 1831, after touring a New York prison that practiced an early experiment in isolation, Alexis de Tocqueville wrote, "This absolute solitude, if nothing interrupts it, is beyond the strength of man ... it does not reform, it kills."

Testifying before the Senate Judiciary Committee earlier this year, University of California psychology professor Craig Haney, an expert on the effects of solitary confinement, described how some prisoners become "so desperate and despondent that they engage in self-mutilation and ... a disturbingly high number resort to suicide.

Indeed, it is not uncommon in these units to encounter prisoners who have smeared themselves with feces, sit catatonic in puddles of their own urine on the floors of their cells, or shriek wildly and bang their fists or their heads against the walls that contain them."

That is awful enough. Even more awful is that some of these prisoners are children. Disturbed, even violent, children who have done, some of them, terrible things, at least terrible enough to have them housed in adult jails and prisons.

But children nonetheless. A chilling new report by the American Civil Liberties Union and Human Rights Watch documents the intersecting trends of juveniles held in adult facilities and adult facilities' increased used of solitary confinement.

"Adolescents can be defiant, and hurt themselves and others," the report acknowledged. "Sometimes, facilities may need to use limited periods or forms of segregation and isolation to protect young people from other prisoners or themselves. But using solitary confinement harms young people in ways that are different, and more profound, than if they were adults."

Some of the juveniles were put in solitary to protect them from being preyed on by older inmates. Others were punished for disciplinary violations such as fighting. These were not temporary timeouts, but stretches that ran to weeks and even months. Of 127 youths contacted by the groups, 49 said they spent a total of between one and six months in solitary confinement before they turned 18; 29 said they spent longer than six months in isolation. In New York City, for example, the average period of punitive solitary confinement for juveniles was 43 days.

The youths interviewed described being kept from seeing their families, denied access to educational materials or books, allowed out only for brief periods to exercise in small enclosures.

"The only thing left to do is go crazy -- just sit and talk to the walls," said one boy held in solitary at a Florida jail at age 16. "It's starting to become a habit because I have nothing else to do. I can't read a book. ... I feel like I am alone, like no one cares about me -- sometimes I feel like, why am I even living?"

Another boy, held in a Michigan jail at 14, described his "stone bed ... a very disgusting slot that they slide food in. The light on 24/7 so you couldn't sleep at all. ... I felt like I was going mad."

This treatment is unconscionable and unconstitutional. Whatever you think about the use of solitary confinement when it comes to adults -- and the evidence suggests that it is both cruel and counterproductive -- it cannot pass the minimum tests of decency to inflict this punishment on adolescents, with their still-developing brains, reduced capacity for impulse control and greater prospects for reform.

The Supreme Court has repeatedly recognized that "children are constitutionally different from adults" when it comes to sentencing. Juvenile murderers cannot be executed or automatically sentenced to life without parole.

Likewise, Congress and the states should act to abolish this gruesome practice. To the extent isolation of prisoners is necessary, it must be proportionate not only to the offense involved but to the age of the offender.