The American Civil Liberties Union and the NAACP announced the suit Thursday against the Ferguson-Florissant School District. It claims the district's at-large elections make it more difficult for blacks to be elected, even though the district serves more black families than whites.
The suit seeks elections where candidates are selected by ward or sub-district.
A school district spokeswoman says the lawsuit is being reviewed.
Race issues have been brought to light in Ferguson since the Aug. 9 shooting death of 18-year-old Michael Brown, who was black and unarmed, by a white police officer. A grand jury decided last month not to charge Officer Darren Wilson with a crime.