This issue has already been decided by the Supreme Court of Canada in 2001, which stated in their decision:
“In light of the serious infringement of privacy and personal dignity that is an inevitable consequence of a strip search, such searches are only constitutionally valid at common law where they are conducted as an incident to a lawful arrest ... conducted at the police station“.
In other words, strip searches can only be legal if done by police after one has been placed under arrest. This did not happen in this case. The police were not called, the child was not arrested and no drugs were found on the child. The family is now suing the school board.
It is not surprising that the Quebec Education Minister is ignorant of this and has defended the school's actions. After all, this is the same Education Minister who doesn't believe that libraries should buy more books!