Parents were arriving at the Carriage Drive campus to pick students up.
Meanwhile, Merrill West High School in Tracy was locked down Friday morning after staff received notice that "something was going to happen" on campus, school officials said.
The Tracy campus was locked down at about 9 a.m. as a safety precaution.
The incident follows other similar scares at schools around the nation in the wake of a massacre earlier this week at Virginia Tech.
On Thursday, schools in Yuba City and Marysville were locked down after a man threatened to carry out killings somewhere in the region. The man turned himself in to police late in the day.
Officials at West High said Friday they contacted Tracy police as soon as they received the new threat.
Tracy school officials said that all students were safe and that there was no need to pull students out of class.