Literature studies have outlined that indoor environmental quality (IEQ) in educational environments can seriously impact students’ learning and cognitive abilities. Research on the combined effects of IEQ domains on cognitive abilities is scarce, especially as regards acoustics and indoor air quality (IAQ). In this laboratory study, 29 university students were exposed to two IAQ conditions which were approximated by means of two CO2 concentrations: 800 ppm (good air quality) and 3000 ppm (poor air quality). For each of them four acoustic conditions, namely quiet, mechanical ventilation noise, babble noise, and birdsongs, were considered. Participants performed a simple calculation task; accuracy in the operations and the time needed for solution (response time) were collected. Data were analysed using generalised linear mixed-effects models by including the main effect of the environmental stressors and their interaction as independent variables. Accuracy was unaffected by environmental stressors, while response time revealed a combined effect of the two domains. Specifically, poor IAQ acted as a trigger, revealing faster responses in the babble noise case compared to quiet and mechanical ventilation. No discrepancies were found in good IAQ conditions. In conclusion, IAQ and acoustics should be considered in combination while investigating cognitive abilities.