Opening the schools is really a math problem: If the general population has a 5% infection rate, then what are the odds that 1 kid in your child's 30 student class is infected?

0.95 ^ 30 that there is no virus = 0.21
Which means a 79% chance that somebody in the class is infected.

How about 1% in the general population? 26% chance somebody is infected.

This is why every epidemiologist, etc. says keep groups small. Having that size group in a closed space for hours with no masks, means 100% transmission to every susceptible person in the room.