The American Humanist Association received a complaint from two Mountain View Elementary parents about the fifth-grade graduation ceremony May 30 in North Greenville University's chapel that included two prayers, said Monica Miller, an association attorney.
North Greenville University is affiliated with the South Carolina Baptist Convention.
"The school's actions were clearly unconstitutional," according to the letter.
"The main problem is that you've got school-aged children attending a school-sponsored event that's supposed to be secular, not only are they confronted with two prayers, but they're also in a building that's surrounded by not just symbolism, but with religious, overtly Christian symbolism," Miller said in an interview. "That's a problem, especially when you've got younger children there."
The parents were "very offended" and "taken aback," she said.
Oby Lyles, spokesman for the Greenville County school district, said the district's attorney was looking into the matter and would prepare a response to the association.
Lyles said principals are provided in-service training and information regarding the First Amendment's Establishment Clause and the need to ensure that school activities do not advance, prefer or promote religion.
"Through those efforts we strive to balance the Establishment Clause with the protected ability for individuals to express private religious speech," he said. "For example, a school should not endorse the use of prayer by students at any school-sponsored event.
"The district will continue to monitor school-sponsored programs to ensure compliance with the law and will take appropriate action if needed."
The letter was addressed to district Superintendent Burke Royster and school Principal Jennifer Gibson.
Gibson could not be reached for comment. A spokesman for North Greenville University could not be reached for comment.
Miller said the association hopes to hear back from the school or the school district within two weeks and that the ceremony at NGU was an isolated incident.
Knowing the school won't do this in the future would prevent legal action, Miller said.