It was just after 3 o'clock, when Toronto Police were called to Michael Power Cathoic High School for reports of a stabbing.
Police say a teen boy was stabbed outside of the school, and managed to make it inside, seeking help from those inside.
It's unclear what led to the stabbing, but officers say they have three people in custody.
When it comes to the condition of the boy, police say they believe his injuries aren't considered life threatening.
The school was placed under a lockdown, while police searched for suspects.