Alexander Youshock, 18, is charged in San Mateo County Superior Court with attempted murder and other felony charges for the Aug. 24 incident at Hillsdale High School, prosecutors said.
At a hearing Friday to receive a third doctor's competency report in response to Youshock's defense attorney Jonathan McDougall's request for competency proceedings, a probation officer announced the doctor needed another week to finish the report.
The first two doctors appointed to evaluate Youshock's competency have disagreed whether he can stand trial, and the third doctor's report is expected to be the tiebreaker.
Youshock has been in custody without bail since he was arrested the morning of the pipe bomb incident. He is being charged as an adult even though he was 17 when he allegedly brought the pipe bombs to school.
Police said Youshock set off two pipe bombs inside a hallway at the high school shortly after 8 a.m. He is also suspected of bringing a chainsaw, a 2-foot sword and eight more pipe bombs onto the campus.
He was arrested after being tackled by a teacher, who along with the school's principal and several other school employees was hailed a hero afterward.
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.
He has pleaded not guilty to all the charges.
The third doctor is expected to present the report June 3.
