With coronavirus cases surging, Montgomery County officials delayed their timeline for bringing the first students back into classrooms to Feb. 1, stepping back from the possibility of opening to small groups of students in special education in mid-January.

When students return to school campuses, they will be phased in, with the first group to include more than 18,600 children in kindergarten through third grade, along with some students in special education and career programs.

But any reopening amid the pandemic is contingent on health conditions in the jurisdiction, under plans adopted Tuesday by the Montgomery County Board of Education.

“I do believe we struck a good balance between wanting our students to get back in school and the health and safety of our students and staff,” said Brenda Wolff, president of the board.

Wolff said that while she knows the decision won’t please everyone, the school system of more than 161,000 students would “continue to be guided by the data and the science.”

The decision comes as the state’s largest school district — also among the largest in the country — remains divided on returning students to classrooms. Recent data showed a sharp spike in failing grades for the Montgomery system’s most vulnerable students for the first quarter.

School officials on Tuesday pointed to a recent survey of parent preferences that showed families were nearly equally split on whether they wanted their children back on campuses or to remain in all-virtual learning.

The more than 38,000 students with parents who did not respond to the survey — 23 percent of enrollment — will be assigned to virtual learning unless other preferences are made clear in coming weeks.

The board also approved changes to benchmarks the school system uses to guide its transition to in-person learning, relaxing its approach to allow more students to return if the 14-day average for new cases per 100,000 county residents is under 15 and the 14-day average test positivity rate falls below 5 percent.

On Tuesday, the two-week average number of new cases per 100,000 residents was nearly 42 and the test positivity rate was 6.2 percent, the school system said.

Critics have been increasingly vocal in their objections to the system’s previous approach, saying Montgomery’s metrics were too strict and left too many children who needed to be in classrooms stuck in virtual learning.

Students in Montgomery County have been out of school buildings since March, when schools shuttered nationally.

“I believe in more acceleration . . . but I’m not willing to throw all caution to the wind,” said school board member Patricia O’Neill, pointing to several other school systems in the Washington region that have retreated from plans for in-person instruction.

School officials urged everyone in the suburban county to work together to slow the spread of the virus. The Feb. 1 target for returning the first students is the beginning of the school year’s second semester.

“It is certainly our hope, all of us, all of the board members and all of the staff, that we can begin to have students experience in-person school opportunities,” Superintendent Jack R. Smith said.

In November, Montgomery’s board gave its approval to a preliminary plan to return children to brick-and-mortar schools, at least part time. Safety measures would be key, including face coverings, social distancing, frequent hand cleaning and other sanitizing.

But coronavirus cases have continued to rise.

Under plans adopted Tuesday, students would come back in phases when health conditions allow, beginning with students in kindergarten to third grade and some in special education and career programs. The next wave to return would include grades four, five, six and 12, as well as prekindergarten. After that would come students in grades eight, nine and 11, and finally those in grades seven and 10.

The school system expects all school buildings to be open and that bus transportation would be provided for those who have requested it.

State Superintendent Karen B. Salmon last week pressed Maryland’s 24 school systems to consider bringing at least some students back for in-person learning. She cited research showing there is not major spread in school buildings and noted the mental health fallout, learning losses and inequities for vulnerable students.

Salmon said students are at greater risk with schools closed.