In a 6–3 decision delivered by Justice Byron White, the Court ruled that the school's search of T. L.

[8][fn 4] Upon opening it, Choplick found a pack of Marlboro cigarettes and rolling paper on top of the purse, which he associated with marijuana use.

[10] Believing a more thorough search "might yield further evidence of drug use", Choplick searched the rest of the purse, revealing a small amount of marijuana, a tobacco pipe, several empty plastic bags, an index card with the names of students who owed her money, and two letters implicating her in dealing marijuana.

's mother brought her to the police station for questioning, where T. L. O. admitted to selling marijuana at the school.

[12] T. L. O. elaborated that she had sold "approximately 18 to 20 marijuana cigarettes for a price of one dollar each" earlier that day.

's purse was acceptable because Choplick "had reasonable cause to believe that smoking, a violation of school policy, had occurred".

The Supreme Court of the United States, in a 6–3 decision issued by Justice Byron White, balancing between the legitimate expectation of privacy of the individual, even a child, and the school's interest in maintaining order and discipline, held for the appellant (the state).

Thus, the vice-principal had reasonable cause to suspect a school rule had been broken, and more than just a "hunch" to search the purse.

In a separate concurring opinion, Justice Lewis F. Powell Jr. (joined by Justice Sandra Day O'Connor) stated that while he agreed with the Court's opinion, he felt that students in primary and secondary educational settings should not be afforded the same level of protection for search and seizures as adults and juveniles in non-school settings.

[26] Justice William J. Brennan, joined by Justice Thurgood Marshall, agreed with the majority's conclusions about the applicability of the Fourth Amendment to school teachers but dissented from the new standard set down by the Court, which he felt was a departure from the traditional "probable cause" approach.

In adopting this unclear, unprecedented, and unnecessary departure from generally Fourth Amendment standards, the Court carves out a broad exception to standards that this Court has developed over years of considering Fourth Amendment problems.

Its decision is supported neither by precedent nor even by a fair application of the 'Balancing test of power' it proclaims in this very opinion.