[Aurornis]

Most studies don't register cognitive changes in the range of 2000ppm. A lot of the military and space studies used exposures multiple times higher than that without registering cognitive problems. It wasn't until you got to very high numbers that they registered any changes.

Only a couple studies purport to show cognitive changes at levels around 2000ppm, and the ones I know of all involve one controversial researcher named Usha Satish.

There are a lot of studies with CO2 levels at 10,000ppm or higher that have failed to find cognitive effect (an example https://pubmed.ncbi.nlm.nih.gov/29789085/). Your 2000ppm classroom air would have been like fresh air relative to the concentrations these studies are looking at.