Energy consumption in school buildings and improving their energy efficiency is an important research issue. This study aims to investigate the energy behaviour of school buildings in Greece, based on their date of construction and technical characteristics, before and after the implementation of various bioclimatic intervention scenarios on them and the subsequent estimation of their cost according to their typology. The method followed is the research and collection of data on the evolution of school buildings over time and their classification into three categories, to determine the most representative in regards to their time period and their technical characteristics. Based on this standardization, their energy situation is assessed with the program of TEE-KENAK and the implementation of the Technical Instructions TOTEE / 2017. Then, scenarios regarding bioclimatic passive interventions in the shell of the buildings and in their electromechanical installation are applied and their energy efficiency is investigated, which improves significantly, especially in older buildings, with a respective reduction in their energy consumption. Finally, the cost of these interventions is calculated, depending on the category of the building and the type of intervention.