That school, along with the nearby St. Mary Elementary and McHugh Public schools, were placed under a hold and secure designation by police as a precaution.
The order was lifted about two hours later.
A hold and secure notice means no one is allowed to enter or leave the schools.
Investigators say the suspect in the attack is also a student at the school.
The injured student suffered non-life-threatening injuries, according to police.
Peel Regional police are looking for a male suspect who is wearing a school uniform, approximately 5' 8" tall, with a slim build.