Energy consumption in Spanish school buildings is higher during spring seasons. Thermal inertia of buildings can help to reduce such consumption, improve comfort, and even replace HVAC systems. This thermal inertia is usually associated to heavy wall construction, but the truth is there are other parameters that can have a significant effect on this property. This paper describes a field case study of school buildings with different types of wall construction, aimed at demonstrating real thermal inertia effects on indoor conditions. Besides air temperature measurements, HAM tools were used to simulate indoor air conditions. Results showed a good agreement between simulated and experimental air temperature results, and that other building construction parameters, such as the use of permeable coverings, may have a large impact on indoor thermal conditions and energy consumption. (C) 2011 Elsevier Ltd. All rights reserved.