THE SUPREME COURT has an opportunity this term to correct one of the uglier mistakes of its recent history: its 1989 decision upholding the death penalty for juveniles. Yesterday the court held oral arguments in a case that asks whether it will continue to stand behind that ruling. It shouldn't. The Constitution's Eighth Amendment prohibits "cruel and unusual punishments." Executing people for crimes committed when they were 16 and 17 is certainly cruel -- a barbaric mistreatment of children, whom the state has a duty to protect. It is also unusual, even more so now than when the court last considered the matter. Even for those who favor the death penalty, killing juvenile offenders should be beyond the constitutional pale.

Formally, 19 states still permit the execution of juvenile offenders. In practice, however, the juvenile death penalty is far more contained than that. Of the 22 juvenile convicts executed since the death penalty's reinstatement, almost 60 percent were put to death in Texas. Only seven states have executed juvenile offenders, and in the past 10 years, only three states -- Texas, Oklahoma and Virginia -- have done so. What's more, since the court's 1989 decision, several more states have set the minimum age for death penalty eligibility at 18, as has the federal government. Juries are increasingly reluctant to impose the death penalty on those who were children when they committed their crimes. And while overseas practice shouldn't bind American constitutional law, it is worth noting the company this country has to keep in subjecting juveniles to capital punishment: China, Congo, Iran, Nigeria, Pakistan, Saudi Arabia and Yemen. The practice simply no longer exists among democratic nations.

Abolishing the juvenile death penalty will not dramatically alter the debate over capital punishment in this country. It will, however, bring to bear against a few outlying states the powerful national consensus that children -- even when they do terrible things -- are different from adults. Insulating them from the ultimate punishment should not be a tough call.