Unfortunately even if you have a "zero sniffles and max masking" policy schools are just a breeding ground for germ transmission. You're usually "infectious" before you're symptomatic, so it spreads like wildfire anyway.
School sicknesses are so common that it might almost be argued that the point of public education is to make sure everyone is exposed to as many diseases as possible.
I completely disagree with this defeatist attitude, and I do not think it is supported by evidence.
Regularly washing your hands reduces spread of the flu by 30%. (Old study, not going to find it.)
I will believe anti-disease spread measures are effective until they are proven otherwise.
> You're usually "infectious" before you're symptomatic
This trait of Covid was what made it unusual. For the flu, the most infectious period days 1-3 with symptoms. ("Period of Contagiousness" in [1]... of course there are exceptions.)
Sure, and you should take reasonable precautions (including not penalizing "sick days" in various ways), but if kids go to school they're going to get sick.
School sicknesses are so common that it might almost be argued that the point of public education is to make sure everyone is exposed to as many diseases as possible.