Marietta City Schools is under fire from civil rights groups alleging that bias over more than a century has held back minority students.

The tiny independent system in Cobb County denies discriminatory behavior.

Two historic civil rights groups — the Southern Christian Leadership Conference and the NAACP — joined with a handful of complainants, including a retired teacher, in a federal complaint.

“Since the inception of Marietta City Schools in 1892, the school district has conducted business through a white lens,” said a statement from the groups before a planned protest Monday. “The past 125 years of the district’s policies and practices have inflicted a blight on minority achievement that stretches to this day.”

Ken Sprague, who retired from teaching math at Marietta High School five years ago, was among the half dozen complainants who sought redress last month through the federal Department of Education’s Office for Civil Rights. He said all the superintendents and most other school leaders, including most of the school board, have been white though most students are black or Hispanic.

Their initiatives, such as the International Baccalaureate program and the way it was implemented, have resulted in segregated classrooms, he said.

“One environment is high expectations, the other environment is low expectations.”

For instance, said Sprague, whose son still teaches in the system, only four black high school graduates from the district met the composite college readiness benchmark on the 2016 ACT. Last spring there were nearly 400 seniors.

The district responded with a statement that all employees are committed to providing a quality education for city students and that there is no discrimination against employees, students or the public on the basis of race, color, religion, national origin, age, disability or gender.

“Every day, all of our employees work diligently to ensure all students have support and access to opportunities that promote academic growth,” the district said.