An Oakland police officer will be stationed Monday morning at a West Oakland elementary school where a third-grader was attacked with a hammer by a parent Friday, officials said Saturday.

The extra security measures come in the wake of the morning assault in a restroom at Lafayette Elementary, when the parent of a second-grader seriously injured a 9-year-old with a hammer in what officials described as a possible act of revenge in a family feud.

"We think this is an absolutely isolated incident, but we want to be on the safe side. ... We'll continue to work with students and staff there throughout the week," said Troy Flint, a spokesman for the Oakland Unified School District. "Ordinarily, that school is very quiet."

The district also brought in a team of counselors and extra administrators to help students and staff, sent a note home to parents and talked to teachers about how to address the incident with students, Flint said.

The attack happened at around 10:50 a.m., when officers responded to reports of an assault at the school, located at 1700 Market St.

Police and school officials would not describe the injuries suffered by the girl but confirmed the suspect used a hammer to injure her.

The girl was taken to a hospital and is expected to recover, Flint said.

The suspect, Hasseemah Diemi, was arrested at the scene with the help of a school security guard, Flint said. She was booked on suspicion of assault with a deadly weapon. Alameda County prosecutors will decide whether to file formal charges.

Diemi's daughter is in second grade at the school, Flint said. The woman is a "known presence" on campus as an informal class volunteer.

The suspect lured the victim from a play area to an outdoor restroom adjacent to the school and a nearby park, Flint said. Inside the restroom, the woman attacked the girl, he said.

"I'm not commenting on the nature of the assault, but the girl was taken to a hospital," Flint said. "It was a serious assault."

The girl was conscious and communicating with rescue workers, he said.

"She's an amazingly resilient girl," Flint said. "That's one small, tiny silver lining in this horrible incident."

Diemi may have been angry Friday over a feud between her family and another family, culminating in the attack on the girl, Flint said.

"The preliminary speculation is that this was part of a family feud and some sort of revenge in the pursuit of that family feud," he said. "There's apparently an ongoing rivalry or feud between families, and this may have been an act of retribution or vengeance as part of that feud."

Parents picking up their children Friday at an after-school program at the campus expressed shock.

"You leave them at school, and you believe they're safe," said Christopher Slaughter, 34, who has a 6-year-old son at the school. "To come to school where little kids are, to commit an act of violence like that, it's terrible."

Alan Johnson, 46, who was picking up his 7-year-old goddaughter, said of the suspect, "That's someone who has the wrong intent in their heart. Whatever is going on, however angry you are, you should not inflict violence on a child. I hope this person is prosecuted and never goes home."