Marcus McLaurin was waiting for recess at Ernest Gaullet Elementary School on Nov. 11 when a classmate asked about Marcus' mother and father, the ACLU said in a complaint.
Marcus responded he had two mothers because his mother is gay. When the other child asked for explanation, Marcus told him: "Gay is when a girl likes another girl," according to the complaint.
A teacher who heard the remark scolded Marcus, telling him "gay" was a "bad word" and sending him to the principal's office. The following week, Marcus had to come to school early and repeatedly write: "I will never use the word `gay' in school again."
A phone message left for Lafayette Parish schools superintendent James Easton was not immediately returned.
The ACLU is demanding the case be removed from Marcus' file and that the school apologize to the boy and his mother, Sharon Huff.
"I was concerned when the assistant principal called and told me my son had said a word so bad that he didn't want to repeat it over the phone," Huff said. "But that was nothing compared to the shock I felt when my little boy came home and told me that his teacher had told him his family is a dirty word."