The district has said the T-shirts were disruptive and therefore a violation of school dress code. The lawsuit filed in federal court also names Webb City High School Principal Stephen P. Gollhofer.
"Because I'm gay, my school is trying to take away my constitutional right as an American to express myself," the student, Brad Mathewson, said in a statement.
"The school lets other students wear anti-gay T-shirts, and I understand that they have a right to do that," he said. "I just want the same right."
The 16-year-old junior started attending the high school this year. On Oct. 20, he came to class wearing a shirt from the Gay-Straight Alliance at his former high school in Fayetteville, Ark.
Mathewson was told either to turn the shirt inside out or to go home and change. Instead, Mathewson traded shirts with a friend, who wore the shirt without incident the rest of the day.
On Oct. 27, Mathewson wore a T-shirt bearing the phrase, "I'm gay and I'm proud." He left school after refusing Gollhofer's request to turn the shirt inside out, and was briefly suspended.
He returned to school Nov. 2 after promising not to wear gay-themed T-shirts until the issue could be resolved.
Ron Lankford, superintendent of the Webb City R-7 school district, said Tuesday afternoon that while he had not seen a copy of the lawsuit, the district plans to contest it.
"I suppose this is why you have a court proceeding," Lankford said. "One side of the story has already been told, and this will be an opportunity to present the side that hasn't been told."
He declined to be more specific.
The ACLU is basing its case on a 1969 Supreme Court ruling that said schools cannot force students to give up their right to freedom of expression (search).