Ms McMillen feared she and her girlfriend would be thrown out of the prom
A school board in the US state of Mississippi has cancelled a high school prom after a female student asked to attend with her girlfriend.
The board said it would not host the event due to "distractions to the educational process".
Student Constance McMillen, 18, said the move was in retaliation for her request to bring her girlfriend to the event and wear a tuxedo.
The school had circulated a memo prohibiting same-sex dates.
Ms McMillen approached school officials shortly before the memo was issued.
According to the American Civil Liberties Union (ACLU), which is backing Ms McMillen's case, the school board told her that she and her partner would not be allowed to arrive at the event together nor would she be allowed to wear a tuxedo, AP reported.
Itawamba County Agricultural High School in Fulton also reserved the right to ask Ms McMillen and her girlfriend to leave if it made any other students feel uncomfortable, the ACLU said.
The ACLU had given the Itawamba County school district until Wednesday to reverse the school's ban on same-sex couples attending proms.
In a statement issued on Wednesday, the board said it hoped that "private citizens will organise an event for the juniors and seniors" instead.
Ms McMillen said cancelling the prom was an act of "retaliation".
"A bunch of kids at school are really going to hate me for this," she told local media.
She also said that when she asked a teacher about the school's ban on same-sex dates at the prom, she was told she had to remember where she was.