It happened around 2:10 p.m. in the parking lot, apparently during a dispute that happened after classes dismissed for the day.
School security responded to reports of an argument among students in the parking lot.
The Spring Valley Police Department School Resource Officer and school security quickly responded and broke up the dispute.
One student was stabbed and a second slashed, perhaps during a struggle. A third student suffered minor abrasions after being punched in the face.
One individual was taken into custody, and an investigation is currently ongoing.
The student with the most severe injury is 19 and was rushed to Westchester Medical Center in stable condition.
The other students with less severe injuries were treated and released at hospitals in Rockland County.
There was a large police presence at the school, and a car with blood on it was taken away on a flatbed truck.
Spring Valley Police detectives and school district security continue to investigate the incident and what led to the altercation.
Anyone with additional information is urged to reach out to police.