Boston Schools benefitted from the actions of two large school districts that represented nearly 25% of all students...and the study employed rigorous "Difference in Difference" analysis with verifiable data for months before the change in masking took place so as to clearly see the effects...tailor made for assessing results of those schools that required masks and those that didn't. Your referenced studies I suspect don't have that degree of rigor...That's why the NEJM study has value and the others you mention don't.