The fight between two male students occurred about 12:15 p.m. on the campus at 1171 El Camino Real, according to the Tustin Police Department.
One of the boys was taken to a hospital in an unknown condition, and the other boy was taken into custody, police said.
Officials did not release their ages or names. The knife has since been recovered by officers.
School officials had students shelter in place, and once the fight was over students were released for the day, police said.
No other injuries were reported. The incident remains under investigation.
City News Service, Inc. contributed to this report.
This is a developing story. This article will continue to be updated as more information becomes available.