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It happened at Castro Valley High School -- now entering finals week, just days before the summer break.
Junior Sakinnah Brown told us her reaction was immediate, as soon as she saw the graffiti Thursday -- a racial slur scrawled on a locker and across some poles at the school.
Classmate Will Sualua was walking with Brown. "We were walking down the hall and she noticed that there was lettering on the poles by the snack bar," he said.
And then it happened again, students sent us photos showing the same phrase written across a mirror in a boys bathroom.
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They say this represents a larger problem.
"There's blatant racism at this school," Brown told ABC7 News. "People say it, people write it, people say it on social media."
"That graffiti was targeting students based on their race and we don't tolerate that," said Superintendent Parvin Ahmadi, who told ABC7 News the district has sent letters home to parents and won't shy away from the issue.
"It isn't something that's isolated to one school, one student, one classroom," Ahmadi said. "I think it's something we need to address all the time."
These students jump-started the conversation with a lunchtime public forum and some messaging of their own.
"I feel like this situation right now, this stuff needs to be talked about, needs to be heard." said student Tia Allen. "People need to be educated about what we have to go through as students, not just being students, but being African-American students."
School officials have yet to identify those responsible for the graffiti incidents.