Aragon High School's day came to a close shortly before 1:30 p.m. and was a normal school day, San Mateo police Sgt. Dave Norris said.
Heading into the school day, however, San Mateo police could be found in and around the campus investigating a threat made through a social media site this week, and ensuring the students' safety.
An undisclosed number of uniformed and plainclothes police officers patrolled the grounds of the school throughout the day in light of the threat.
Norris said nothing happened at Aragon, but officers will report there again on Friday, and will be making passing checks on the campus throughout the weekend.
Additionally, officers will be keeping a close eye on the other San Mateo schools Friday as a precaution, he said.
Police detectives are continuing to investigate the case, but have not identified a suspect, Norris said.
A female student at the school notified school administrators Wednesday morning about the threat, made on an anonymous "confessions" page she created on a Google doc, San Mateo Unified High School District Associate Superintendent Kirk Black said. School staff notified the district, which in turn alerted San Mateo police, Black said.
The threat, described as "rambling," specifically mentioned Thursday's date, and some parents elected to keep their students home for the day, Black said.
Today's attendance figures for Aragon were not immediately available this afternoon.
Black said administrators ensured parents prior to the school day that the threat had "very little credibility" to it.
Although the belief the threat was smoke and mirrors, Black said district officials took it seriously and used an "abundance of caution."
Officers were on the campus at the start of the school day, along with school administrators and counselors, and students were monitored as they entered the school, Black said.
As a precaution, a private security firm conducted surveillance at the campus overnight, he said.
Black said the student who reported the threat had created the "confessions" page on the Google doc for Aragon students, and copy-and-pasted posts onto a Facebook page she created.
The student told administrators that posts were coming in so rapidly, she hadn't noticed the threat until it was already on the Facebook page, Black said.
She has since removed the post from the page, he said.
San Mateo police officers and detectives went to the school, located at 900 Alameda De las Pulgas, immediately after getting word of the threat, according to Norris.
The district normally has one student resource officer for its seven high schools, Black said.
The San Mateo-Foster City School District was also notified of the threat, as one of its schools, Baywood Elementary School at 600 Alameda De Las Pulgas, is just a few blocks away, Norris said.
Anyone with information about the threat is asked to call San Mateo police at (650) 522-7700