https://www.sciencedaily.com/releases/2021/01/210121132231.htm

Experts say that school reopening policies currently lack a rigorous evidence base -- leading to wide variation in policies around the world, but staging cluster randomized trials (CRT) would create a body of evidence to help policy makers take the right decisions.

The pandemic's rapid onslaught meant many public health policies had to be put into practice quickly despite uncertainty about the risks from SARS-CoV-2 and the effectiveness of various prevention measures.