According to Keith, the district attorney's office declined to file charges against the other two students.
Two girls and one boy were charged, Keith said.
The attack happened at about 12:50 p.m. Monday. Tiffany Carrico, a music teacher who has been with the district for about five years, had been assigned to keep students out of a particular classroom, police said.
When she denied access to a group of students, they allegedly threw rocks at her. As a larger group gathered, the students pushed Carrico to the ground, El Cerrito police Sgt. Shawn Maples said.
A vice principal at the school witnessed the attack and came to Carrico's aid. Carrico eventually escaped from the students and ran to her classroom, Maples said.
School district spokesman Marin Trujillo said Carrico was placed on paid administrative leave while police and the school district investigated the incident.
She was not seriously injured in the attack, police said.
The incident brought attention to an ongoing dispute between the school district and the El Cerrito Police Department.
Maples claimed that the principal and vice principal at the school have seemed unwilling in the past to report criminal activity on the campus.
However, Trujillo claimed that the school district had been working closely with the Police Department to ensure safety at the school.
Pixie Hayward Schickele, president of the United Teachers of Richmond, the union representing teachers in the district, said last week that, unfortunately, she was not surprised by the attack.
The school district has allegedly been failing to discipline students in an effort to lower its suspension rate, Schickele said.
"Teachers have brought these concerns to the district administration and they've just been disregarded," Schickele said. "It's outrageous."
Since the incident, the school district has contracted with the Police Department to have a school resource officer stationed on campus during school hours, Trujillo said.