Since late fall, 60,000 students and teachers across Greenville County, South Carolina, have been filing into the classroom for school the old-fashioned way: in-person, five days a week.

They've done it, Greenville superintendent Burke Royster said, by enforcing mask wearing, hand washing and social distancing -- mostly by about 3 feet with plexiglass barriers when 6 feet isn't possible -- using high-quality ventilation and launching their own contact-tracing program.

Royster said he believes his schools have lower transmission than its surrounding community -- a finding that is supported by research.

"I think it simply reinforces that this is a workable, viable solution," Royster said of his school's mitigation methods.

Greenville County is one of many examples across the U.S. of schools that have charted their own path forward since fall in the absence of a clear federal standard on what it means to reopen a classroom safely.

That all changed Friday when the Centers for Disease Control and Prevention for the first time issued specific steps schools could take depending upon their level of viral transmission in the community.