As the coronavirus’s delta variant continues to rage in Florida, leading to record-high hospitalizations, more than 160,000 students in Palm Beach County returned to the classroom this week with no mask mandate due to a statewide ban.

It took just two days for school officials to send 440 students home to quarantine, the county’s interim superintendent, Michael Burke, told MSNBC on Thursday. Burke noted that 37 students and 14 employees were infected and blamed Republican Gov. Ron DeSantis for allowing students to opt out of wearing masks.

“The governor has got to take responsibility for establishing the ground rules we’re operating under,” Burke said. “This ability for families to opt out is leading to more cases, which will ultimately send more kids home and deprive them of that traditional classroom experience.”

Palm Beach County is one of more than a dozen school districts already sending students and teachers home to quarantine within days of starting the new school year. A review of local media reports by The Washington Post found that more than 10,000 students and staff members across 14 states have been exposed to the virus since school started.

Experts warn that they are seeing an increasing number of children infected with the highly contagious delta variant. Hospitalization rates for children have also increased, although doctors note that the symptoms are not as severe as those affecting adults.

But the knowledge that students, especially those under age 12 who are ineligible for the coronavirus vaccines, are more likely to experience covid-19 symptoms than last year is daunting for school officials. Jack Catrett, the superintendent Talbot County, Ga., south of Atlanta, said the schools there shut down after at least a dozen students tested positive. The school district is one of four in Georgia to suspend in-person classes.

“The difference now in this outbreak that we see, than the outbreak that happened last school year, is that this seems to be more centered on kids ... rather than adults, so that scares me to death,” Catrett told WTVM.

Warren County Public Schools in Kentucky, which has more than 17,000 students, reported 95 cases, according to WBKO. More than 700 students and staff members there are also in quarantine. The high number of infections led the superintendent to implement a mask mandate.

And the entire fourth-grade class at Patrick Henry School of Science and Arts in Richmond is quarantined after the school reported four positive cases, according to the Richmond Times-Dispatch.

A parent in Reno, Nev., sent their child to Marce Herz Middle School two days after the child tested positive for the coronavirus, the Washoe County Health District announced Wednesday. The student exposed more than 80 peers. A county spokesperson told the Reno Gazette Journal that unvaccinated students now must stay home until Aug. 20. Those who are vaccinated and have no symptoms are allowed to return to school.

In Mississippi, which has one of the lowest vaccination rates in the country with only 35.5 percent fully inoculated, at least 1,000 students and school employees have tested positive, according to the state’s department of health. More than 4,400 students are quarantining.

In Arkansas, where the governor signed a bill preventing school districts from mandating masks — a decision he says he now regrets — about 1,200 students have been quarantined since the start of the school year after more than 100 students and staff members tested positive, WREG reported.

“If we had masks on our students and our faculty from day one, instead of having 1,200 quarantines, we would have experienced roughly 100,” Glen Fenter, the superintendent of the Marion school district, told the station.

As of early Thursday, 665 students and staff members in Kershaw County, S.C., are in quarantine after at least 128 students and 23 staff members contracted the virus, according to the district’s covid-19 dashboard. About 10,500 students go to school there. The state’s education superintendent, who said she is concerned by the student quarantine numbers, urged lawmakers to reconsider the state’s ban on mask mandates.

The trend is especially troubling to school district leaders in states where governors have forbidden mask mandates. But some have chosen to defy the orders. Hours after the school year began, the superintendent of the Dallas Independent School District announced Monday that schools would require masks. Two days later, Dallas County Judge Clay Jenkins (D) announced further mask requirements in the county and agreed that students and teachers there must wear face coverings in schools.

As school district leaders in some of the major cities in Florida moved to ignore DeSantis’s executive order banning mask mandates, the governor has threatened to withhold their salaries. The Biden administration has since explored whether it can give unused stimulus funds to educators who defy the order.

In Oklahoma, Santa Fe South Schools Superintendent Chris Brewster, who invoked a mask mandate in schools despite a statewide ban, said he has considered the consequences.

“I am aware that I am personally responsible for either decision,” Brewster wrote in a letter to families in the district. “If this decision keeps a single member of our community from suffering serious health issues or death, it is worth it a thousand times over.”

Gina Harkins contributed to this report.