Virginia’s largest school district will begin offering four days a week of in-person instruction this month, following a recent change in federal guidelines on social distancing inside classrooms.

In mid-March, the Centers for Disease Control and Prevention revised its recommendation for the appropriate spacing between students inside school buildings from six feet to three feet under certain conditions. Based on that guidance, Fairfax County Public Schools will shrink its social distancing requirements inside some elementary school classrooms, officials announced Monday.

Middle and high schools will remain at six feet, however, because under CDC definitions, Fairfax County still qualifies as experiencing a “high” level of community transmission of the novel coronavirus. The school district will nonetheless “expand capacity for in-person instruction” at middle and high schools, officials said Monday, permitting the jump to four days a week of face-to-face schooling.

Space between teachers and students will remain at six feet at all levels.

Overall, the changes will permit Fairfax to phase students at all grade levels in to four days a week of classroom learning over the next month. Currently, students in the Northern Virginia district who chose in-person learning are going inside classrooms two days a week.

The district is prioritizing students who “are experiencing the greatest learning challenges,” officials wrote in a post on the school district’s website. Those children will begin four days per week of in-person learning this week and next.

Other students who are already participating in in-person learning will begin heading inside classrooms four days a week starting the week of April 20. Fairfax will “determine availability based on each school’s staffing and space capacity,” officials wrote, and will contact families who qualify for this expansion of in-person instruction during the week of April 13.

A Fairfax spokeswoman said that “it is hard to put an exact number on how many students . . . overall” will transition to four days a week of in-person learning because capacity varies by school.

“School leadership will be working hard to minimize disruption,” officials wrote. “We appreciate everyone’s patience and support.”

Fairfax, which enrolls 180,000 students, spent much of the past two months returning nearly half of its student body — approximately 84,600 children — to classrooms under a model based on six feet of spacing. The remaining families had previously opted to keep learning virtually through the end of the semester.

Fairfax officials have said that all students will be able to attend five days a week of in-person learning starting next fall. Schools Superintendent Scott Brabrand has said that the district will offer a “limited” virtual program, probably restricted to students who must remain ­online-only for medical reasons.

In switching to four days a week of in-person learning, Fairfax is following in the footsteps of nearby Loudoun County Public Schools, which announced last month — before the CDC published its revised guidance — that it was preemptively switching to three feet of distancing inside classrooms and would launch four days a week of in-person learning starting April 20.

Other Northern Virginia systems have been slower to disclose how the shift in federal guidance is altering their plans. Officials with both Arlington Public Schools and Alexandria City Public Schools said they would give updates on the distancing question after their respective spring breaks, which end this week.