The published evidence that was available in 2003 provided some grounds for suspecting that the thermal conditions and air quality of most present-day school classrooms might be having negative effects on children, but no conclusive evidence that this included negative effects on their ability to perform schoolwork.

The problem was that although the symptoms experienced by children with allergies and asthma had been shown to be made worse by the dust and air pollutants present in school classrooms, leading to increased absenteeism in this sensitive sub-group, and although respirable dust had been shown to induce symptoms even in healthy children, there was no direct evidence that upgrade measures that reduced the concentration of dust and air pollutants in classrooms (e.g. providing more outdoor air or operating efficient air cleaners), would progressively improve the average performance of schoolwork by a given group of children. Similarly, although children in an air-conditioned classroom had been shown to perform schoolwork slightly better than children in an adjacent classroom who were deprived of this advantage during a period of warm weather, such a difference might have been due to the frustration and envy of the control group so there was again no direct evidence that an upgrade that reduced classroom temperatures would progressively improve the performance of schoolwork by a given group of children.