President Biden's plan to accelerate the reopening of K-8 schools faces major challenges from a still out-of-control pandemic and more contagious coronavirus variants.

Why it matters: The longer American kids miss in-person schooling, the further they fall behind. But the uncertain state of the science on the role young children play in the pandemic continues to complicate efforts to reopen schools.

Driving the news: On Thursday, Biden signed an executive order laying out his administration's response to COVID-19, which builds on a proposed coronavirus relief package that would include $130 billion in additional aid for K-12 schools.

• That money can be used to improve ventilation, reduce the size of in-person classes to emphasize social distancing, and purchase more personal protective equipment.

By the numbers: In his inaugural address, Biden said "we can teach our children in safe schools." But with the country still recording nearly 200,000 new COVID-19 cases a day, we're still a long way from that goal.

• The federal government currently doesn't maintain data about how many American kids are learning at home versus in school — though Biden's executive order calls for the creation of just such a database — but a tracker maintained by Burbio indicates less than a quarter of U.S. students are back in full-time traditional classes.

Details: The state of the science around the safety of opening schools during the pandemic remains in flux.

• Researchers have concluded that young children — while not invulnerable to the disease — are about half as likely to be as susceptible to COVID-19 infection as are adults.
• Scientists aren't certain why that is, though one reason may be that young children have fewer ACE2 receptors in their respiratory tract, which the virus uses to latch onto cells.
• Researchers studied nearly 100,000 students and staff at dozens of schools in North Carolina and found only 32 infections were recorded in school between reopening in August and the end of October.
• If schools in the area had the same level of transmission as the surrounding community during that time, researchers expected the students and staff — who wore masks and remained socially distant in the classroom — would have recorded 800–900 cases.

But, but, but: Other studies indicate transmission can and does happen in schools, especially as overall levels of the virus in the community rise.

• Data from New York and Texas — two of the few states where decent information is available about possible classroom transmission — indicates that in recent months, teachers and other staff where school buildings are open have higher COVID-19 infection rates than the surrounding community.
• In European countries — where schools have remained open at higher rates than in the U.S. — political leaders have more recently moved to shut classrooms, in part out of early reports that more contagious new variants of SARS-CoV-2 may spread more easily among young children.

The catch: The sheer size of the U.S. outbreak means the virus is spreading faster nearly everywhere, and poor contact tracing means it's difficult to be certain that teachers and staff are contracting COVID-19 in open classrooms, versus the larger community.

• Teachers in cities like New York where schools have partially opened are also being tested more frequently, which could help explain the apparent rise in infection rates.
• And a report this month from Public Health England that relied on detailed contact tracing of about 20,000 people infected with the B.1.1.7 variant showed that children were no more likely to spread the new variant than the previous iteration of SARS-CoV-2.

What they're saying: “I still say exactly what many people have said for the past few months — that schools should be the last thing to close,” Helen Jenkins, an infectious disease expert at Boston University, told the New York Times.

Be smart: With the right social distancing and the right protective equipment, in-person schooling for young children — who also happen to be the group that struggles the most with remote education — should still be relatively safe.

• But politics, even more than science, appears to be driving the decision to open or close schools.
• Schools in Republican-led states like Texas and Florida have been more likely to remain open over the past several months, even amid major outbreaks, whereas public schools in Chicago have remained shut since March, and teachers there are threatening a walkout over plans to partially reopen.

The bottom line: Whether schools open or close during the pandemic, someone will lose.

• Open classrooms, and teachers will be at some risk, especially if community transmission remains high and schools lack protective equipment.
• Keep them closed, and students will suffer, with the most disadvantaged children bearing the heaviest burden.

Go deeper:The COVID-19 learning cliff