ATLANTA  A county school system in metropolitan Atlanta on Thursday became the nation’s first in nearly 40 years to lose its accreditation, and the governor removed four of its school board members for ethics violations.

The school system in Clayton County, just south of the Atlanta city limits, was ruled unfit for accreditation by the Southern Association of Colleges and Schools, one of the nation’s six major private accrediting agencies, after school board members failed to meet the group’s standards for leading a school system.

An investigation by the agency found that county officials had not made sufficient progress toward establishing an effective school board, removing the influence of outside individuals on board decisions, enforcing an ethics policy or meeting other requirements for accreditation, Mark A. Elgart, the chief executive of the association, announced Thursday at a news conference.

County officials said they were planning to appeal the decision.

The loss of accreditation could impair the ability of Clayton County students to attend some colleges and earn scholarships. It could also prevent teachers from receiving benefits if they change school systems, and could mean a loss of money for pre-kindergarten education.