Sheriff's officials confirmed a stabbing took place at about 12:45 p.m., and the male student was transported to an area hospital with non-life-threatening injuries.
The student was said to be working out in the weight room when an altercation took place before he was stabbed with an undetermined object, according to officials.
Authorities said at least three people took off running, but were later detained for questioning. It was not known whether those detained were also students.
Chaffey Joint Union High School District Superintendent Mat Holton said the unidentified victim was cooperating with police to help identify the suspects.
"Immediately, we brought more resources in here to clear the campus, actually both campuses, and look for additional subjects. And we detained two at the time, and like I said, it could lead to more...," said one sheriff's official.
Nearby Lightfoot Elementary School was also placed on lockdown while authorities searched for those involved in the incident. The lockdowns on both campuses were lifted shortly before 3 p.m.