The incident happened on West 56th Street outside the School for Environmental Studies Thursday.
Police say 19-year-old Teddy Beckles was stabbed at least twice during an argument outside the school.
The teenager lived on his own in the Bronx, working at McDonald's while going to school.
"Teddy was a decent character," friend Shay Palmer said. "He was always fun. He played his music loud. He was a great guy."
Just before school let out, Beckles' girlfriend got into an argument with some of the other students.
Eyewitness say they saw three men jump Beckles just down the street from the school, stabbing him repeatedly.
Police were searching the area for the knife as they tried to piece together the details of exactly what led to the attack.
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