The two students were fighting in the hallway of Lindenhurst Middle School when the boy stabbed his rival in the leg with a 6-inch knife, Suffolk County Police said.
A 17-year-old girl used a box-cutter during an argument with two fellow students, a 17-year-old girl and 18-year-old girl at Uniondale High School, police said.
The boy was stabbed by a 12-year-old student during an altercation early Monday afternoon, police said. School officials said Tuesday they believe it was "an isolated incident."