Noel Buehler, superintendent of the Oak Grove Union School District, said two males in a gray Dodge Ram pickup who were being chased by sheriff's deputies pulled into the parking lot of the school at 8285 Hall Road at about 10:25 a.m.
One exited the truck and ran across a soccer field at the rear of the campus and into residential yards, Buehler said. The suspect was not armed, he said.
Deputies chased the suspect, and a sheriff's helicopter also responded, Buehler said.
Students at the school were outside on a break at the time and were instructed over a public address system to immediately go to their next period's class, Buehler said.
The students were all inside classrooms within seven minutes and remained there until about noon when the school was informed all was clear, Buehler said.
The school, located in unincorporated Sonoma County, has 430 students in grades 6-8.