First, second and third grade students reportedly carried pictures of O.J. Simpson, Dennis Rodman and Ru Paul at last Friday's celebration. Other pictures included President Barack Obama and the Rev. Martin Luther King.
Lorraine Abner's letter did not name the celebrities.
"Unfortunately, questionable decisions were made in the selection of noteworthy African American role models," the letter said. "As the principal, I offer my apology for these errors in judgment."
Some civil rights activists and groups have criticized some of the choices, saying they made a mockery of black history and reinforce racial stereotypes. They are asking that the teachers, who are white, be fired and that the principal, who was not at the school Friday, be reprimanded.