The 12:50 p.m. incident occurred at the end of the lunch break toward the north end of the Elsie Allen campus in an area that houses Midrose, a small alternative school for students trying to make up academic credits. The suspect, whose name was not released because he is a juvenile, attends Midrose, which has about 70 students.
During the brief and bloody attack, another student tried to intervene and "pull the teacher and the other kid apart," Linscomb said.
That student wasn't hurt in the scuffle, and the teacher and the boy who attacked him both fled out of the classroom and into a courtyard. The teacher called 911. Students who witnessed the attack told police they saw the boy head north to a gate in the campus fence that led into the Bellevue Ranch neighborhood, Linscomb said.
Police found the teen about three blocks north of campus at a relative's home on Silver Spur Drive.
Officers found what appeared to be the boy's bloody clothes in the neighborhood along the youth's "escape route," Linscomb said. Late Wednesday, police had not yet found the pencil, he said.
A man who answered the door where the boy was taken into police custody said he was a relative and the boy lived elsewhere in Santa Rosa with his parents.
The man, who didn't want to be identified, said his family was struggling to understand what took place with the youth and that he was "sorry it had gotten to this point."
Police don't yet understand what might have motivated the attack, Linscomb said. The boy didn't have a known history of violence, he said.
The stabbing elicited a large-scale police response.
The entire 980-student campus was on lockdown. Students were quarantined in classrooms with the blinds drawn, lights off and doors locked. They were instructed to stay quiet.
Wednesday afternoon, an officer placed yellow police tape around beams in the northern courtyard outside a door under the Midrose High School sign as a police dog sniffed around the bushes.
The Sonoma County sheriff's helicopter flew circles above the eerily quiet campus.
Abigail Suarez, 16, said she and her classmates in a public safety class sat silent, some doing homework but most typing messages to each other and to their families on their cellphones.
"My Dad texted me after the school called," Suarez said, referring to an automated message school officials sent out to parents. "I was a little nervous."
Oman Morales, 15, said he was about to take a test in a human anatomy class, but it was postponed.
"I was never scared because I knew what was happening," Morales said.
At just after 2 p.m., Stablein informed teachers via the campus intercom that lessons could resume, but that students were required to remain in class.
"You must keep all students in the classroom at this time," she said over the loudspeaker. "You may turn on the lights and you may return to instruction, but you need to keep all students inside the classroom."
"If any student witnessed the incident that happened at lunch today... you are to tell your teacher immediately," she said.
Many students contacted home by cellphone and text message, prompting parents and relatives to begin lining up outside the school almost two hours before the final bell, worried about the students inside.