 This study investigated the effect of carbon dioxide levels during sleep on the next day cognitive performance of young school children. The results showed no significant effect of CO2 levels during sleep on next day cognition. However, the children had higher sleep efficiency when exposed to higher levels of CO2. This could be due to chance, since the children were awoken in the morning and spent time in well, ventilated rooms before being tested. Further research is required to determine whether or not this effect is real. This article was authored by Frida Bedjer-Klausen, Ali Amity, Soren K. Jairgaard, and others.