The Hardin County School District has agreed to allow students to display their support for gays and lesbians.
The assertion came in a letter from the district's attorney to the nonprofit Southern Poverty Law Center.
The center had complained last month that students were being prohibited from publicly supporting gay rights in school.
That was after several high schools students said an assistant principal told them that T-shirts such as one with a rainbow flag violated the dress code policy by promoting sex.
The school district attorney writes that students can peacefully display "non-vulgar expressions in support of LGBT people."
The letter also affirms that slogans such as "Lesbian and Proud" and "I Love My Gay Friends" are not vulgar or sexually suggestive.