The board was under pressure to respond after eighth-grade students were asked to do research and write an essay explaining whether they believe the Holocaust was an actual event or fictional.
"This asinine assignment was either unconscionable idiocy or insidiously evil. Either option is incomprehensible," Tressy Capps of Rialto said to the board during the meeting.
"This is not about anti-Semitism. This is about hate," another man said.
One college student brought along photos taken after she met a Holocaust survivor.
"This is something that everyone should know about," she said.
The board went into a closed session after hearing from several speakers. When they returned, a statement was read apologizing to anyone offended by the assignment.
"This project commenced and turned into a horribly inappropriate assignment," said Board President Joanne Gilbert.
The interim superintendent says teachers will undergo immediate sensitivity training.
"That holocaust denial exists is a slander against every victim of the Nazis, dead and alive," said Rabbi Abraham Cooper of the Simon Wiesenthal Center.
A group of students and teachers had earlier planned to visit the Museum of Tolerance in June.