Police say he was stabbed in the neck and the stomach and taken to Kings County Hospital in critical condition.
Authorities were searching for a suspect, another student. He was initially described as a light skinned male, about 16 years old, around 5-foot-5 and 150 pounds.
The school was placed in lockdown. Students were held for two hours before they were allowed to go home.
The school has metal detectors at the entrance, and it was not clear how the weapon got into the building.
The large school, which houses 1,530 students, has had its share of violence.
In Dec. 2006, a bleacher-clearing brawl broke out at a basketball game. Numerous students were injured, and the incident led to the basketball team's suspension from play for the rest of the season.
The school hosted a community meeting last week in opposition to gangs.
