Public schools are filled with eager, fresh-faced youngsters, and prisons contain many rough-looking adults with uninviting personalities. But put aside that difference and you find some important similarities between the two places -- government-run facilities where individuals are held for a specific number of years without their consent, at the mercy of their custodians.

For years, the Supreme Court has been doing its best to further blur the distinction by giving public-school officials the same powers as the warden of San Quentin. So it was a mild surprise last week to learn there are some abridgments of freedom and invasions of privacy inflicted on children that the justices will not tolerate.

That's the good news for youngsters. The bad news is unless an administrator makes you take off your clothes, you're probably out of luck.

One day in the fall of 2003, a middle-school student in Safford, Ariz., was caught with contraband ibuprofen, which she said she had gotten from Savana Redding. The 13-year-old Savana was called to the office, where she denied knowing anything about the pills and agreed to a search of her belongings.

When it turned up nothing, an administrative assistant took her to the nurse's office and told her to remove her jacket, socks and shoes. Still no pills.

That would have been the perfect moment for a sudden burst of common sense, inducing the school officials to admit defeat and let the girl get back to algebra. But the needed epiphany did not come to the adults. They ordered Savana to take off her shirt and pants -- a step that also proved unavailing.

Were they done? No, they were not. In their relentless quest for illicit Advil, the officials refused to let considerations of modesty be an impediment. They insisted that Savana pull her bra and underpants away from her body to prove she was not hiding pills there. Again, they got nothing.

Last week, though, they got a rebuke from the Supreme Court. It has given principals and teachers great latitude in imposing control on children. But even justices who were indulgent with past government intrusions gagged at the image of officials peeking into an adolescent's most private areas.

Justices Samuel Alito and Ruth Bader Ginsburg don't agree on many things. But they and six other justices (Clarence Thomas being the exception) joined in a decision that rejected abusing public-school students in the name of protecting them.

The Fourth Amendment, they noticed, says individuals shall not be subject to "unreasonable searches and seizures," and this search was flagrantly unreasonable. The mere possibility of finding pills in underpants is not enough, wrote Justice David Souter, to "make the quantum leap from outer clothes and backpacks to exposure of intimate parts."

School administrators might be forgiven for not knowing that. After all, the Supreme Court had previously allowed them to force students to undergo drug testing as a condition of participating in any extracurricular activity. Making students who have done nothing wrong produce a urine sample under the monitoring of a teacher, it insisted, was "not significant" as a breach of privacy.

The court had also permitted schools to search a kid's locker, backpack and purse on even modest suspicion that some trivial school rule had been violated.

Justice John Paul Stevens complained that under these decisions, "a student detained by school officials for questioning, on reasonable suspicion that she has violated a school rule, is entitled to no more protection under the Fourth Amendment than a criminal suspect under custodial arrest." The Constitution's privacy protection, he said, has become "virtually meaningless in the school context."

Stevens did not exaggerate. Even in this case, the court was willing to tolerate making a 13-year-old girl strip to her underwear. It was the "exposure of intimate parts," not the exposure of everything else, that caused the justices to bridle. But if a more dangerous item had been sought or if there had been reason to think she was actually hiding a pill in her bra, the majority indicated, the search might have been perfectly acceptable.

So there's still a difference between the rights we afford students and the rights we afford prison inmates. Just not a very big one.