Two school districts in North Dakota had a different policy on masking. One did mask and the other did not. The schools had similar demographics. The rate of COVID infections in both districts were statistically equal. The district that required masking abandoned the policy. That district did not have an increase in COVID infections. This was not a double blind study. In effect it was a study with a control group.
Link to article https://www.americanexperiment.org/north-dakota-study-masks-in-schools-hardly-impacted-covid-spread/ Masks do not work for COVID! The CDC knew masks were virtually worthless but foisted them on us for political reasons. It is all about control.
https://www.americanexperiment.org/north-dakota-study-masks-in-schools-hardly-impacted-covid-spread/