A photo that showed two students holding up a sign as part of a prom proposal left parents, students and teachers at a Southern California high school in disbelief after it was shared on social media.

The sign held by Palos Verdes High School students reads, "You are a racist, but I would give anything for you to go with me to prom." It includes highlighted letters that spell out a racist slur.

The boy and girl appear to be laughing in the photo, which was posted to Twitter and Instagram.

The girl pictured in the photo posted an apology online late Wednesday, saying she initially didn't notice the racial slur, and she doesn't find it funny.

The post reads, "I am so ashamed my face is behind this. If you know me as a person you know I do not discriminate against anyone. I would never want this kind of reputation for myself and for my school. My school has taken action, and I have been punished, along with three other people who were involved in this situation."

The school did not reveal what kind of punishment the students were facing.

In an initial statement released to students, principal Allan Tyner called the slur a "slang term," for which he apologized later Wednesday.

"We were made aware today by some of our students of an invitation that incorporated a slang term for African American and features two of our high school students," principal Allan Tyner said in a statement. "We have been in touch with the identified students and their families to inform them that we are forming a response and anticipate severe consequences. In accordance with our values and expectations for respectful conduct in our district and at PVHS, this sign is unacceptable."

Tyner said the school is trying to determine whether other students were present at the time the photo was taken. Tyner said he was heartened by responses to the sign on social media from students and their families, many of whom denounced the students' behavior.

"It makes me feel small, honestly, to know that there are students on my campus who think that that is acceptable, who think that's appropriate, and think that word is just a word that can be thrown around like that," said student Ryan Pascal. She also said she immediately penned a letter to administrators, expressing her disgust.

Student Ryan Pascal also wrote to administrators, expressing what it felt like to see the classmates' photo.

"I saw the promposal of that, and it didn't sit well with me," said junior Joey Quinn. "I know a lot of my friends are nothing like that and I just don't think it represents our student body at all."

"It makes me feel small to know that there are students on my campus who think that that's acceptable," said Ryan Pascal. "Who think that's appropriate. Who think that that word is just a word that can be thrown around like that."

School officials went class to class Wednesday to discuss the post.

"Racist words and racist acts have no place in our school community," Tyner said. "We will rise above this, learn from this, and be a better school community because of it."

Two representatives from the NAACP also came to campus late Wednesday and left angry. They said they were turned away because the principal was too busy to talk with them and would schedule a future meeting.

"I believe information and education on other races and what’s not a slang word but a painful racist word would educate these students on how painful this whole situation is," said Dr. Cheyenne Bryant of the San Pedro and Wilmington chapter of the NAACP.

The high school's prom is scheduled for Saturday. Palos Verdes High School is on the Palos Verdes Peninsula, located about 30 miles southwest of downtown Los Angeles.

NBC4's Jonathan Lloyd contributed to this report.