In an 8-1 ruling, the justices said that Safford Middle School officials violated the Fourth Amendment ban on unreasonable searches with their treatment of Savana Redding. The court ruled that the officials could not be held financially liable but left it to lower courts to decide if the school district could.

While children’s advocates and civil liberties groups cheered the decision, others suggested the high court may have created further problems for school systems by failing to make clear exactly when school administrators can strip search students and when they can’t.

“The court seems to think it made things clearer, but I don’t think they did,” said Dan Capra, a Fordham University law professor. “Officials now know they can’t do exactly what was done in Safford. But what if there is any change of material fact in the circumstances?”

Redding was 13 when the educators in rural eastern Arizona conducted the search in 2003. They were looking for pills — the equivalent of two Advils. The district bans prescription and over-the-counter drugs without advance permission, and the school was acting on a tip from another student.

The search of Redding’s backpack and outer clothes was permissible, the court said. But the justices said that officials went too far when they asked to search her underwear.

A 1985 Supreme Court decision that dealt with searching a student’s purse had found that school officials need only reasonable suspicions, not probable cause. But that ruling also warned against a search that was “excessively intrusive.”

“What was missing from the suspected facts that pointed to Savana was any indication of danger to the students from the power of the drugs or their quantity, and any reason to suppose that Savana was carrying pills in her underwear,” Justice David Souter wrote in Thursday’s majority opinion.

“We think that the combination of these deficiencies was fatal to finding the search reasonable.”

Redding, now in college, said she was pleased with the court’s decision. “I’m pretty excited about it, because that’s what I wanted,” she said. “I wanted to keep it from happening to anybody else.”

“The court’s decision sends a clear signal to school officials that they can strip search students only in the most extraordinary situations,” said her lawyer, Adam Wolf of the American Civil Liberties Union Foundation.

In a dissent, Justice Clarence Thomas said the search had been legal and the court previously had given school officials “considerable leeway” under the Fourth Amendment in school settings.

In this case, officials had searched the girl’s backpack and found nothing, Thomas said. “It was eminently reasonable to conclude the backpack was empty because Redding was secreting the pills in a place she thought no one would look,” he said.

Thomas warned that the majority’s decision could backfire. “Redding would not have been the first person to conceal pills in her undergarments,” he said. “Nor will she be the last after today’s decision, which announces the safest place to secrete contraband in school.”

The court also ruled the middle school officials could not be held liable in a lawsuit for the search. Different judges around the nation have come to different conclusions about immunity for school officials in strip searches, which leads the Supreme Court to “counsel doubt that we were sufficiently clear in the prior statement of law,” Souter said.

“We think these differences of opinion from our own are substantial enough to require immunity for the school officials in this case,” Souter said.

School lawyers praised the decision not to hold the school officials financially liable.

But “the majority opinion offers little clarification of the applicable Fourth Amendment standard while unduly limiting the ability of school officials to protect students from the harmful effects of drugs and weapons on school campuses,” said Matthew W. Wright, lawyer for the school district.

The justices said lower courts would have to determine whether the Safford Unified School District No. 1 could be held liable.

“While today’s decision was not an unqualified triumph for Savana Redding, she has secured a victory for schoolchildren nationwide,” said Nan Aron, president of the Alliance for Justice.

Several states ban strip searching students, including California, Washington, Iowa, New Jersey, Oklahoma, South Carolina and Wisconsin.

A schoolmate had accused Redding, then an eighth-grade student, of giving her pills.

The school’s vice principal, Kerry Wilson, took Redding to his office to search her backpack. When nothing was found, Redding was taken to a nurse’s office where she was told by a female administrative assistant and the school nurse to take off her shirt and pants. She then was told to move her bra to the side and to stretch her underwear waistband, exposing her breasts and pelvic area. No pills were found.

A federal magistrate dismissed a suit by Redding and her mother, April. An appeals panel agreed that the search didn’t violate her rights. But last July, a full panel of the 9th U.S. Circuit Court of Appeals found the search was “an invasion of constitutional rights” and that Wilson could be found personally liable.

Justices John Paul Stevens and Ruth Bader Ginsburg dissented from the portion of the ruling saying that Wilson could not be held financially liable.

“Wilson’s treatment of Redding was abusive and it was not reasonable for him to believe that the law permitted it,” Ginsburg said.

The case is Safford Unified School District v. April Redding, 08-479.