Around 11:15 a.m., the victim, a 17-year-old senior, was in the school cafeteria when another student attacked her, punching her and knocking her to the ground, Principal Erik Faulker said.
School security personnel separated the girls, and the victim was airlifted to John Muir Hospital after emergency crews indicated she may have suffered head injuries.
The student was admitted into the hospital's Intensive Care Unit where it was determined she had suffered a concussion and is now recovering, the principal said.
Police arrived on campus and arrested the victim's alleged attacker, a 16-year-old junior at the school, on suspicion of felony battery, according to Faulkner and police Chief Bani Kollo.
The student's name was not released since she is a juvenile.
The principal said police also considered a second student as a potential suspect but that her involvement in the attack has not yet been determined.
Authorities are continuing to interview students about the incident today.
"We're still separating fact from fiction," Faulkner said.
The principal said he has learned that Thursday's attack stemmed from an incident Wednesday when the victim and suspect bumped into one another in a school hallway.
According to Faulkner, the girls exchanged words and parted ways, but that evening, the suspect allegedly sent messages via text or email to other students about a plan to attack the victim. She and the victim also exchanged messages via online photo-sharing and social networking website Instagram, he said.
For the school of more than 2,500 students, the incident has underscored the role of social media in exacerbating the types of conflicts long experienced by high school classmates.
"The interchange happened the day before and we know it was escalated that night via social media - in the past that wouldn't have happened," he said.
Faulkner said that since the incident, faculty members are taking the time to address ways to handle conflict and reminding students, "once you put it out there you can't take it back."