The Centers for Disease Control and Prevention issued new guidelines for schools Friday that give students who have been vaccinated the option of going maskless this fall while their classmates who have not had shots continue to wear face coverings.

The much-awaited easing of pandemic rules for kindergarten through 12th grade follows the opening of vaccine eligibility this spring to anyone 12 and older.

But it also arrives after some states and school systems have gone their own way — lifting mask mandates and forging ahead with plans for a highly anticipated school year that is just weeks away.

In Texas, mask mandates were ended in public schools under the governor’s order. In Miami, the familiar face gear is optional this fall. In Marietta, Ga., masks will no longer be required inside buildings or outdoors.

School systems across the country began announcing a few months ago that fall would mark a full return of students to brick-and-mortar schools five days a week — in a major effort to revive at least some pre-pandemic normalcy.

“We recognize that we’re about a month out from school starting in some areas,” said Erin Sauber-Schatz, a CDC official who oversaw the school guidance. “But we wanted to do a re-review . . . to make sure that the recommendations that we were making for the fall school year were based on science and the best available evidence that we have at the time.”

The guidance, which is not binding, reflects many of the same concepts that the CDC released in April and May for the broader population.

But it may fuel a new round of political debate about masking and vaccinations — heralded by some, derided by others — as divisions carry over to schools.

And practically speaking, it may be difficult to implement: It does not spell out how schools would collect accurate information about who is vaccinated — and thus able to go without a mask — and who is not.

“The school has to decide if and how they’re able to document vaccination status,” Sauber-Schatz said. If that is not possible, she said, “the safest thing to do to protect those people who are not fully vaccinated” is to go with a universal policy requiring masks.

The start of school in August is expected to be far different from a year ago.

Vaccinations are widely available now. Just 13 percent of the nation’s counties are recording high levels of community transmission, compared with 90 percent in December.

But coronavirus variants, including the highly transmissible delta variant, are a significant unknown for many parents and teachers.

CDC officials say they remain confident in the effectiveness of their “layered” approach to safety in schools — using multiple strategies at once, including masking, distancing, screening, contact tracing, ventilation upgrades and staying home when sick.

“We really have limited data on transmission of this variant in school settings, but we also don’t have any data to suggest that the layered prevention strategies would be ineffective,” Sauber-Schatz said.

Still, for some educators, uncertainties about exactly who is vaccinated may translate into a desire for masks for all.

According to CDC data, 24 percent of people ages 12 to 15 nationally are fully vaccinated, along with 36 percent of those 16 and 17 years old. Parts of the Washington suburbs have much larger percentages of teenagers at least partly vaccinated.

Vaccinations are not yet available for children under 12, but executives from Pfizer-BioNTech and Moderna have said that data showing whether their vaccines are effective in younger children is expected by fall.

Becky Pringle, president of the National Education Association, called the new guidance “an important roadmap for reducing the risk of COVID-19 in schools.”

Noting the spread of the delta variant, she said in a statement that schools should be “consistently and rigorously” using all recommended safety practices, including “requiring masks in all settings where there are unvaccinated individuals present, and ensuring adequate ventilation, handwashing, and cleaning.”

April Jones, a parent in Maryland, said the mask issue could not be more important for her and several other parents she knows. Her first-grade son has asthma and would be at greater risk if schools stopped requiring face coverings, she said.

“I’m terrified that they are going to decide that elementary school children don’t need to wear masks,” she said. “There are a lot of people who feel their children should be vaccinated before the masks come off.”

Sonia Vigilante, another Maryland parent, said she was pleasantly surprised that the guidance allowed for vaccinated students to go maskless, which she would love to see in her K-8 Catholic school. But how the guidelines play out is unclear.

“The guidance kind of gives a lot of room for interpretation,” she said.

While masking was a major change in CDC guidelines, the recommendations emphasized that in-person learning is a “priority” for the coming school year, regardless of whether all prevention strategies can be implemented.

It said local jurisdictions should keep a close eye on vaccination rates, community transmission, outbreaks and screening results, as safety measures are weighed or scaled back.

Physical distancing was a touchpoint, too, with the guidelines recommending at least three feet between students in classrooms, but allowing for greater flexibility. In schools where not everyone is vaccinated, it said, distancing should happen to the extent possible but “schools should not exclude students from in-person learning to keep a minimum distance requirement.”

Instead, it says, other prevention strategies, including indoor masking, could be used to help compensate.

The CDC previously revised its school guidelines in March, saying three feet of distance between students was sufficient for all elementary and most middle and high schools.

Daniel Domenech, executive director of AASA, the school superintendents association, said school district leaders have been opening schools for vaccination clinics over the summer and supporting efforts to provide access for middle and high school students.

The new CDC guidance is a reinforcement of that message, he said.

Still, the guidelines could produce complications if middle or high schools are left to sort out who is vaccinated and who should be masked. “It’s an organizational nightmare, no doubt about it,” he said.

But as many considered the implications of the guidance, Education Secretary Miguel Cardona reiterated in a statement that the top priority in 2021-2022 is getting students back into classrooms and school buildings to learn.

With federal funding through the American Rescue Plan, he said, “schools have access to unprecedented resources to implement health and safety measures to best accommodate students for full-time in-person learning, and to address our students’ social, emotional, and academic needs.”

Lena H. Sun contributed to this report.