(CBS News) FOREST, Va. - Eight-year-old Sunnie Kahle likes to keep her hair short, wear boys' clothes, collect hunting knives and shoot her BB gun.
"She's a pure, 100 percent tomboy," said her great-grandfather Carroll Thompson, who along with his wife Doris adopted their granddaughter's child.
But to Timberlake Christian School administrators, the second-grader's boyish ways warranted an ultimatum: Start acting like a girl or find another school.
The Thompsons found another school, but they didn't go quietly. After being told by lawyers that they have no grounds for a lawsuit because Timberlake is a private school, the Thompsons have gone public with their complaints, reported by CBS affiliate WDBJ earlier in the week.
"I don't see nothing Christian about it," 66-year-old Carroll Thompson said in an interview at the family's house just outside Lynchburg, home of Liberty University, the Christian school founded by the Rev. Jerry Falwell.
Doris Thompson, who's 69, said she was stunned when she received a letter last month saying the school can deny enrollment to applicants for condoning "sexual immorality," homosexuality or alternative gender identity.
Principal Becky Bowman wrote that "we believe that unless Sunnie as well as her family clearly understand that God has made her female and her dress and behavior need to follow suit with her God-ordained identity, that TCS is not the best place for her future education."
Doris Thompson said Sunnie knows she is a girl and has never, to her knowledge, wished she were a boy.
Other disputes over gender expression at school have made headlines recently, including a demand, later rescinded, that a 9-year-old North Carolina boy cease carrying a My Little Pony backpack to school. But that case and others involved public schools rather than private religious academies that are not subject to anti-discrimination laws.
After a television news report about the Thompsons created a social media frenzy, the school retained the legal arm of Liberty University to tell its side. Mat Staver, founder and chairman of Liberty Counsel, said there is more to the situation than the Thompsons are saying.
"This is not at all about how she is dressing or she is going through a phase," Staver said in a telephone interview.
However, he said confidentiality laws prevented him from being more specific and school officials would rather not try to rebut the Thompsons' allegations. Earl Prince, an administrator at the school, also declined to discuss what prompted Bowman's letter.
Doris Thompson said she is unaware of anything, other than Sunnie's appearance and tomboy ways, that would prompt the school's action. She said Sunnie made good grades, was well-behaved and got along with the other children. New classmates would sometimes ask if she were a boy or a girl, but she would answer and that would be the end of it, Thompson said.
Bowman acknowledged in her letter that the school's position doesn't stem from Sunnie's grades or "general cooperation with school rules."
Staver said school officials were dismayed that the Thompsons chose not to resolve the issue with them privately. He said school officials would like to have Sunnie back.