It is kind of obvious that mask should make a difference. especially if we are talking respirator masks (N95/Ffp2/Kn95 etc) that are designed to protect the bearer from patogens like viruses. What we have sort of lacked is a real world comparison between a larger number of schools that keeps mask requirements and schools that remove mask requirements. And the result is clear: it makes a big difference. The first link is to the Time article about the NEJM published study.
https://time.com/6231516/universal-masking-in-school-works-new-data-shows-how-well/
https://www.nejm.org/doi/full/10.1056/NEJMoa2211029?query=featured_home
