This study found mask mandates don't corelate with covid transmission - not because masks don't work, but because mandates didn't have an effect on behavior. Where masks were mandated, there was typically already high mask usage, and people who weren't already wearing masks continued not wearing masks. The study found, overall, that a 100% masks population would have 25% lower transmission than a 0% masked population. Not a silver bullet, not the primary driver of the course of the epidemic, but better than nothing. And wrt to the new school mandate, that's far more enforceable than a general population mandate and should have a bigger impact on rate of mask usage compared to the alternative. Other studies have found lower levels of exhaled viral material in the air, and lower rates of disease transmission with animal subjects when infected air was "breathed" on them with and without masks. Now, spending 6-8 hours in a room together is masking going to make a
substantial difference in how much it spreads in schools? I don't know. Masks were always most effective as shorter term protection when you had to be around people while mostly trying to social distance. I'm hopeful this wave passes rather quickly, and this can be a short term measure, but the costs of the measure are very low. We need in person schools for our kids, most kids aren't yet eligible to be vaccinated, and even if only slightly effective, it's one of the few measures we have available at this point for kids.