With the start of classes weeks away and debate intensifying about mask mandates in schools, Maryland’s largest district opted for the cautious way forward, requiring that face coverings be worn by all.

The decision in Montgomery County Tuesday comes a day after neighboring Prince George’s County did the same, requiring masks regardless of vaccination status.

School leaders in Montgomery County cited a string of reasons for the decision, including emerging variants, a rise in coronavirus cases and advice from the American Academy of Pediatrics, which has recommended universal masking in schools for everyone over age 2.

Shortly after the county school board voted to support the approach, the Centers for Disease Control and Prevention announced a change in federal guidance: Now guidelines recommend face coverings be required inside schools in the fall.

The shift by the CDC follows the rise of the highly contagious delta variant, which is said to account for the vast majority of new cases nationally.

“I believe they should still wear masks, especially with this delta variant,” said Brenda Wolff, school board president. “I think that’s going to be the safest position for everybody.”

Wolff pointed out at the Tuesday board meeting that the school system brought 26,000 students back into school buildings over the summer and — with a mask mandate — counted only 13 positive cases as of last Friday, a ratio she considered excellent.

“I think that’s actually due to the mask-wearing,” she said.

The rollout of vaccinations also figured into the 161,000-student school system’s decision. While vaccinations are available for those ages 12 and older, not everyone has received shots — and the youngest children at school are not yet eligible.

When school begins on Aug. 30, Montgomery County — and school systems across Maryland and the country — expect to be open five days a week for full-time instruction inside bricks-and-mortar schools.

Under the new guidance, Montgomery County students would not have to wear masks when they are outdoors, but those who are unvaccinated are strongly encouraged to keep covered anyway. Everyone must wear masks while riding on school buses.

“I know the community is eagerly awaiting a full return to five days a week as normal as possible, and I realize masks are not 100 percent normal in the way we operated before, but health and safety needs to be a priority,” said school board member Patricia B. O’Neill (District 3).

Board Vice President Karla Silvestre pointed out that the decision doesn’t mean that the requirements won’t change during the 2021-2022 school year. Working with health officials, school leaders will continue to evaluate the issue, she said.

“As things improve and our health agencies and experts give us advice, then we can change this mandate,” she said.

The decisions this week arrived on the heels of state health and education department guidance issued Friday that left each school system to decide the question but “strongly” recommended unvaccinated students protect themselves with masks.

The state leaned heavily on CDC guidance for its guidelines. With the shift by the CDC on Tuesday, it was unclear whether there would also be a shift by the state.

Maryland health officials said Tuesday that they are reviewing the most recent iteration of CDC guidance and will continue to closely monitor key health metrics.

Some parents have opposed requiring masks for students in the fall, saying that transmission in schools is low and that students who have gotten vaccinations should be rewarded for their efforts.

On the other side, some parents have said that they would only feel comfortable with children back at school if masks were required to offer another layer of protection against the spread of the virus as cases climb and as a full return to school means less physical distancing.

Montgomery officials said they recognize that the county has had great success with vaccinations, but at the same time many thousands of students do not have shots.

They also said they lack an effective system for monitoring vaccination status of students, teachers and staff members, and then enforcing mask requirements according to whether each person is immunized.

The countywide council of PTAs was advocating an evidence-based, transparent approach to the decision-making, based on expert advice and health metrics.

Even if teens are vaccinated, their younger siblings may not be inoculated, said Cynthia Simonson, president of the countywide PTA council. “We should reevaluate at regular intervals,” she said.