The last student killing inside a New York City public school was on February 26, 1992, when a 16-year-old and a 17-year-old were shot dead in a Brooklyn high school by a 15-year-old.
Laboy remained in critical but stable condition at St. Barnabas Hospital in the Bronx.
"We believe that this argument has been going on for maybe two weeks, and it escalated today after some back-and-forth into the classroom", Chief of Detectives Robert Boyce told reporters on Wednesday.
Schools Chancellor Carmen Farina said she is heartbroken by the violence. Chief Boyce added that it appeared the three students involved had been in a dispute since school started this year.
Authorities say an 18-year-old is in custody in connection with the stabbing at Urban Assembly School for Wildlife Conservation, a combined middle and high school that shares a building with elementary school P.S. 67 on Mohegan Avenue.
The effort reflects a growing interest in NY and beyond in establishing charter schools that enroll students from a mix of backgrounds, which research suggests can benefit students and is considered one remedy to school segregation.
Cedeno faces charges of attempted murder, manslaughter, attempted manslaughter, two counts of assault and two counts of criminal possession of a weapon, the NYPD said. NewsCopter 7 flying over the sceneThe 18-year-old used a scissors to stab a 16-year-old and a 15-year-old.
While school safety agents raced to the room and the teachers and students tried to stop the bleeding, a counselor confronted Cedeno in the hallway and he handed over the blade, police said.
About 20 students had assembled for history class when the fight erupted at 10:45 a.m., Boyce said. Cedeno then took himself to the assistant principal's office, where police were called, and he was arrested.
"And less than half of students polled at the school past year - 47 percent - said they felt safe on campus, well below the city average", the report says. The school doesn't have metal detectors.
Cedeno was placed under suicide watch and held without bail in the murder of 15-year-old Matthew McCree and the stabbing of a second youth as horrified students in their history class watched helplessly. "I guess he did that kind of to scare them off, not to actually hurt anyone", she said. She plans to pull her daughters out of school. On Thursday, metal detectors and additional school security officers will be made available for random screenings at the school.