The U.S. Supreme Court struck a blow for common sense late last month when it ruled that school officials’ strip search of a 13-year-old girl was unconstitutional. The case involved Savanna Redding, an honors student at an Arizona middle school with a zero-tolerance policy on drugs. When another student alleged in 2003 that Ms. Redding had given her prescription-strength ibuprofen, school officials checked the girl’s backpack and outer clothing.

A school nurse then ordered Ms. Redding to strip and pull her underwear away from her body, exposing her breasts and pelvic area. No pills turned up, but Ms. Redding was so shaken by the experience she never returned to school. Her mother sued the officials and the district.

In an 8-to-1 decision, the high court found Ms. Redding’s treatment excessively intrusive, and a violation of the 4th Amendment prohibition on unreasonable searches. Though that protection is more limited in school settings, it is basic enough that many states and school districts ban strip searches outright. The court’s lone holdout, Justice Clarence Thomas, warned that students will now know exactly where to hide forbidden drugs and other contraband. But, balanced against the kind of humiliation Ms. Redding endured, it appears an acceptable risk. And in any case, effective school disciplinarians have found other ways of spotting drug problems and enforcing the rules.

As Justice Ruth Bader Ginsburg has pointed out, 13-year-old girls can be very sensitive about their bodies. They should not face degrading treatment in the name of what has become, in too many school districts, an overzealous war against drugs. Writing for the court’s majority, outgoing Justice David Souter said that in the Redding case, school officials plainly overreacted. They had no evidence that the type and quantity of drugs at issue posed a serious danger to students. Nor did the officials have strong grounds for believing that Ms. Redding was carrying pills in her underwear.

Critics grouse that the court has done little to clarify just when a strip search in the schools might be acceptable. The answer would appear to be: seldom. For when, except in extreme cases, is a strip search of an adolescent not “excessively intrusive,” the standard set forth by the court as long ago as 1985?

Justice Souter noted that at the time the search occurred, the law was somewhat confusing. The court therefore threw out the lawsuit against the officials involved. Justices Ginsburg and John Paul Stevens disagreed on this point but were outvoted. Nevertheless, Ms. Redding still received a good measure of justice, for herself and students across America. Going forward, more school officials will think twice about ordering students to disrobe.