In a 6-3 decision, the Supreme Court ruled in favor of New Jersey and the school, and against T.L.O. Justice White wrote the majority opinion. The majority concluded that school officials do not need a warrant to justify a search as long as the search was reasonable under the circumstances. Justices Brennan, Marshall and Stevens dissented.

The Fourth Amendment’s prohibition against unreasonable searches and seizures applies to public school officials because they act under the authority of the state. In addition students have a reasonable expectation of privacy for the property they bring with them to school. They have not “waived all rights to privacy in such items merely by bringing them onto school grounds.” 

However, the justices said the privacy interest of students must be balanced against the interest of teachers and school officials in maintaining order and discipline in school. Trying to achieve a balance between these interests, the Supreme Court ruled that school officials should not be required to obtain a warrant to conduct a search of a student suspected of breaking school rules because this would “unduly interfere with the maintenance of the swift and informal disciplinary procedures needed in the schools.” 

The Court decided that schools officials do not need to have probable cause to believe that a student has violated school rules in order to initiate a search, even though probable cause is required for police to initiate a search of children or adults outside of school.  Instead, school officials are only required to have a “reasonable suspicion” that a student has violated school rules in order to search that student. A search will be deemed reasonable if, when it is started, “there are reasonable grounds for suspecting that the search will turn up evidence that the student has violated … either the law or the rules of the school.” In addition, the scope of the search must be “reasonably related to the objectives of the search and not excessively intrusive in light of the age and sex of the student and the nature of the infraction.” The Court concluded that “the legality of a search of a student should depend simply on the reasonableness, under all the circumstances, of the search.”

Applying this standard to T.L.O., the Court ruled that the search was reasonable. It was reasonable for the vice principal to believe that T.L.O. had been smoking in the bathroom in violation of school rules because a teacher witnessed it. Thus the vice principal had adequate grounds to search T.L.O.’s purse for cigarettes. While doing so, he came across evidence suggesting that T.L.O. was selling marijuana in the school. This gave him grounds to search the rest of her purse for drugs. 

In his dissent, Justice Brennan first argued that the same probable cause standard that is applied outside of schools should be applied inside schools. The Fourth Amendment states that “the right of the people to be secure … against unreasonable searches and seizures shall not be violated.” According to Justice Brennan’s interpretation, the Fourth Amendment explains what it means by “unreasonable” by specifying that “no Warrants shall issue but upon probable cause.” Thus, searches that take place without probable cause, including those based only on “reasonable suspicion,” are unreasonable, and violate the Fourth Amendment.

Justice Stevens also dissented. Like Justice Brennan, he believed that the Court’s new standard of “reasonable suspicion” was inappropriate. Instead of allowing school officials to search a student based on the reasonable suspicion that the student was breaking a school rule, Justice Stevens would require that the student be suspected of “violating the law or engaging in conduct that is seriously disruptive of school order, or the educational process.” Smoking in the bathroom was not a “violent or disruptive activity,” he argued, so an immediate search was unnecessary.