Police responded to Woburn Collegiate Institute on Ellesmere Road, just east of Markham Road, around 3:20 p.m.  on Monday.
According to police, the victim was shot in front of the school.
Emergency crews arrived and rushed the boy to hospital where he was later pronounced dead.
Toronto police identified him Tuesday as 18-year-old Jefferson Peter Shardeley Guerrier of Toronto.
After the shooting, a 15-year-old boy went to a nearby hospital with gunshot wounds.  He was taken to another hospital where he is now in stable condition.
Investigators described the shooting suspect as a teenage boy with a thin build who wore dark clothing.
In a letter sent to students and their families Tuesday, the principal of Lester B. Pearson Collegiate Institute identified Guerrier as a former student at that school.
“We know you will join us in expressing our deepest condolences to Jefferson’s grieving family, friends, and former teachers and classmates,” Principal Anthony Hack wrote in the letter.
“Jefferson attended Lester B. Pearson CI from 2017 to 2022 and will be greatly missed by our school community.  As a student he participated in the Pearson Band and the Skateboarding Club.  His playful and cheerful nature endeared him to staff and students alike.”
It was not immediately clear if the other victim attended Woburn CI or why Guerrier was at the school when he was shot.


“I THOUGHT IT WAS FIRE” 
The fatal shooting occurred near the end of the school day Monday afternoon and put the school on lockdown, with some students scrambling.
“I heard three shots.  Then I saw the whole school running back and then I just took off home trying to stay safe,” said one student.
Another said the shots sounded like firecrackers.
“At first we thought it was firecrackers,” he said.  “We tried to run and then we saw people running.  So we just ran for our safety.”
Police began escorting students out of the building around 4:30 p.m.  after they had been put on lockdown for about an hour.
Speaking outside the school Tuesday morning, TDSB Director of Education Colleen Russell-Rawlins told reporters that support staff are on scene to speak with teachers and students and will remain available as long as needed.
“We’re all here to listen to their concerns and answer their questions very promptly,” he said.  “We also have extra adults in the building today.  But they know they can count on the people they see every day to support them.
“Whether it’s school security or vice principals, our kids and youth, their teachers — they’re all here because we know that when students are in trouble, when they need help, the people they go to are in this building every day .  And so we can prevent issues like we’ve seen here.”
Hack said support staff will also remain available at Lester B. Pearson CI for as long as necessary.
Russell-Rawlins called the killing on school grounds “a horrific tragedy” and said the board would “consider very carefully what needs to be done here and in all our schools to continue to provide safety and support for students” after the police investigation.
He said a “multi-pronged” approach was needed to prevent violent crime at school, including action by the school board and various levels of government.
Police are asking anyone with more information to contact investigators or call Crime Stoppers anonymously.