The basic right to healthy indoor air has been emphasized almost two decades ago by the World Health Organization (WHO), 1 and then, the improvement of indoor air quality (IAQ) was included in the regional priority goals of the Children's Environmental Health Action Plan for Europe (CEHAPE) and adopted by the Fourth Ministerial Conference on Environment and Health in 2004. 2 Children, one of the most vulnerable groups, spend approximately 6-9 h per weekday in primary school buildings in Europe. Accordingly, several national and international research projects have already been conducted in the past two decades to investigate the association between the concentration of indoor air pollutants and the health outcomes for children at public settings and to promote the health and well-being of children.The HESE study (Health Effects of the School Environment;2004 was the first European project, which provided data on both IAQ and health effects with a wide geographic coverage. 3 In total, twenty-one schools located in five countries were investigated and several IAQ-related problems were identified,