Alexander Robert Youshock appeared in court at 1:30 p.m., handcuffed and dressed in a yellow jail sweatshirt. He remained silent throughout the brief hearing.
Police said Youshock set off two pipe bombs inside a hallway at the high school shortly after 8 a.m. on Aug. 24. He had also allegedly brought a chainsaw, a 2-foot sword and eight more homemade pipe bombs onto the campus.
He was arrested after being tackled by a teacher. No one was injured.
Youshock is charged with two counts of attempted murder, two counts of exploding a destructive device with intent to commit murder, one count of possession of a destructive device in a public place, one count of use of explosives in an act of terrorism, and two counts of possession of a deadly weapon.
His attorney, Jonathan McDougall, who was appointed to represent Youshock by the county's private defender program, requested that Judge Mark Forcum set further arraignment for Youshock in four weeks.
Assistant District Attorney Karen Guidotti, who is prosecuting the case, asked that the arraignment be delayed by only two weeks, and Forcum compromised by setting a date three weeks from today.
He also kept Youshock's bail status set at no bail. He has been in custody at Hillcrest Juvenile Hall since his arrest.
San Mateo Police Chief Susan Manheimer said at a news conference the day after the pipe bomb incident that Youshock's "sole intent was to kill, injure or commit mayhem to as many students, staff and faculty as possible," and that the motive was "self-construed revenge."
Guidotti said the San Mateo County District Attorney's Office decided to charge Youshock as an adult because of the planning that went into bringing 10 homemade pipe bombs, a chainsaw and a sword onto campus.
His age was also taken into account, she said, noting that Youshock is about eight months shy of turning 18.
Extra counselors have been on hand at Hillsdale High School since last week's incident and are expected to remain through this week, San Mateo County Union High School District spokesman Kirk Black said today.
After that, the school will have its usual counselors available for students. The district is expected to implement an employee assistance program as well to offer support to school staff, he said.
Black said the teachers have been helping students move past the ordeal.
"The teachers are monitoring the students," Black said. "If they see signs that they're acting a little different or that they were bothered by what happened, they either discuss it with the student or provide them with counseling information."
Youshock is scheduled to appear in court again on Sept. 23 for further arraignment.