Here’s an interesting recent study showing the hidden impact of high carbon dioxide levels, this time in office buildings and schools, on cognitive function. 
Elevated carbon dioxide may impair reasoning: Insufficient ventilation allows exhaled gas to build up indoors, diminishing decision-making abilities.  According the Janet Raloff at ScienceNews: “The work assessed decision-making in 22 healthy young adults. Their performance on six of nine tests dropped notably when researchers raised indoor carbon dioxide levels to 1,000 parts per million from a baseline of 600 ppm. On seven tests, performance fell substantially more when the room’s CO2 was boosted to 2,500 ppm, scientists report in a paper to be published in Environmental Health Perspectives.

I use CO2 monitoring equipment with my students regularly and we observe carbon dioxide levels rising substantially when students enter a class, routinely exceeding 1000 ppm.  Perhaps, this is another reason students learn better in small classes (in big, well ventilated rooms).  

Sounds familiar?  It might if you’d read this study by Paola Domenici et al (2011) in Biology Letters: