The high school received a bomb threat by phone at about 2 p.m., forcing students to evacuate to the football field while bomb-sniffing dogs from the Alameda County Sheriff's Office investigated, Lampel said.
By 4:15 p.m., the school buildings were 80 percent clear and no explosives had been detected, Lampel said.
The evacuation, which had just been rehearsed during a drill last week, was calm and orderly, according to Lampel.
"The kids knew exactly where to go, they just it the other day," she said.
The students were dismissed from school at 2:45 p.m., and parents were notified of the situation.
The incident is still under investigation.
