https://adc.bmj.com/content/early/20...ld-2022-324172

Conclusions We found no significant differences in SARS-CoV-2 transmission due to FCM mandates in Catalonian schools. Instead, age was the most important factor in explaining the transmission risk for children attending school.

As the authors note, their results "are similar to other studies analysing the impact of mask-wearing policies for students in educational settings."