changes to the school ventilation system?...desk spacing? If nothing ever changed, I'd say you/they were lucky. It doesn't take a Dr. Fauci to figure out that putting 20+ unvaccinated people close together in a small room for 5-6 hours for months on end is a Coronavirus' dream environment...ready made viral transport to all those more vulnerable adults the kids will come in contact with.
Sorry to keep bringing it up, but the MIT report that Baron provided speaks directly to this issue of School Rooms and infection rates...you should dig it out with the "Search" engine and read it...no way you open a school w/o the "adjustments" recommended in that report.