Effect of classroom air quality on students' concentration: results of a cluster-randomized cross-over experimental study

To assess the effect of indoor air quality as indicated by the median carbon dioxide (CO2) level in the classroom on the concentration performance (CP) of students, a cross-over cluster-randomized experimental study was conducted in 20 classrooms with mechanical ventilation systems. Test conditions worse (median CO2 level on average 2115 ppm) and better (median CO2 level on average 1045 ppm) were established by the regulation of the mechanical ventilation system on two days in one week each in every classroom. Concentration performance was quantified in students of grade three and four by the use of the d2-test and its primary parameter CP and secondary parameters total number of characters processed (TN) and total number of errors (TE). 2366 d2-tests from 417 students could be used in analysis. In hierarchical linear regression accounting for repeated measurements, no significant effect of the experimental condition on CP or TN could be observed. However, TE was increased significantly by 1.65 (95% confidence interval 0.422.87) in worse compared to better condition. Thus, low air quality in classrooms as indicated by increased CO2 levels does not reduce overall short-term CP in students, but appears to increase the error rate. Practical Implications This study could not confirm that low air quality in classrooms as indicated by increased CO2 levels reduces short-term concentration performance (CP) in students; however, it appears to affect processing accuracy negatively. To ensure a high level of accuracy, good air quality characterized, for example, by low CO2 concentration should be maintained in classrooms.