The victim, a first-grader, was standing in line on the playground near her classroom about 1 p.m. when the 9 mm round struck her abdomen, San Pablo police acting Sgt. Scott Cook said.
She was not seriously injured, though plenty frightened.
"All of a sudden she grabbed at her stomach and said she felt a sensation in her tummy area," said Adrianne Rosal, a yard supervisor and parent at the school. "We thought the girl got hit by a rock or something. She said something like, 'Teacher, something hit me.'"
She bled from a cut on her stomach, Cook said. Another student found the round sitting next to her.
Its pristine condition and other physical evidence suggest the gunman shot into the air far from the school, well beyond the effective range of the weapon, Cook said. Police surmise the round might have been launched from a slingshot or similar device.
It perforated the girl's skin but did not penetrate far into her body, police said. Paramedics took her to Children's Hospital Oakland, mostly as a precaution, police said.
"We do not believe the shot was fired anywhere in the immediate area," Cook said. "We had officers canvass the blocks around the school, and they did not find anything. There was also an officer in the area at the time who did not hear a shot."
Administrators put the school on lockdown for a half-hour while police investigated.
West Contra Costa school district spokesman Paul Ehara said an extra counselor will work at the school this week.
"The safety plan was put into action really quickly," Ehara said.
Dover is not the first West Contra Costa school campus to suffer an unintended shooting in recent years. On the first day of the 2006-07 school year, officials locked down Nystrom Elementary School in Richmond after rounds from a street shooting passed through a classroom.
"It doesn't matter where you are nowadays," Rosal said of stray bullets. "It's getting more and more frequent."