The girl, identified in court papers as C.H., says she asked the principal at Bridgeton High School last month for permission to join in the Pro Life Day of Silent Solidarity.
She planned to remain silent, except when called on in class. She also wanted to wear an arm band with the word "life" on it and to hand out anti-abortion pamphlets.
The student says the school rejected the idea just before the Oct. 20 protest, saying she couldn't do anything "religious."
Her lawsuit was filed Friday in U.S. District Court by a lawyer hired by the Alliance Defense Fund, a Scottsdale, Ariz., organization.