April 25 (Bloomberg) -- Canadian police can't conduct random searches in schools, even at a principal's invitation, because such measures violate students' rights to privacy, the country's highest court ruled.

In a 6-3 decision, the Canadian Supreme Court upheld the acquittal of an Ontario student who was charged with possession of marijuana and psilocybin for the purpose of trafficking after police conducted a random search at a school using sniffer dogs.

``Students are entitled to privacy in a school environment,'' Justice Louis LeBel wrote for four judges on the court in Ottawa. Two others, including Chief Justice Beverley McLachlin, dismissed the appeal for different reasons.

The principal of St. Patrick School in Sarnia, Ontario, invited police to conduct a search in 2002, Justice Marie Deschamps said. Students were confined in their classes while a dog sniffed backpacks in the school gymnasium. The dog reacted to one backpack and police, without a warrant, opened it and found the illicit drugs.

A youth, identified only as A.M. in court documents, was charged. The trial judge found that police conducted unreasonable searches and dismissed the charges. The Court of Appeal for Ontario upheld the decision.

``Teenagers may have little expectation of privacy from the searching eyes and fingers of their parents, but they expect the content of their backpacks not to be open to the random and speculative scrutiny of the police,'' Justice William Ian Binnie wrote.

Deschamps disagreed, writing that the accused's expectation of privacy wasn't ``objectively reasonable,'' because the dogs were used to search the premises, not the students.

The case is Her Majesty the Queen v. A.M., File 31496, Supreme Court of Canada (Ottawa).

To contact the reporter on this story: Joe Schneider in Toronto at jschneider5@bloomberg.net.

Last Updated: April 25, 2008 13:10 EDT