The present paper presents the results of the application of cluster analysis in the energy rating ofschool buildings. A complete program on energy and environmental quality of school buildings wasundertaken by NKUA in collaboration with the School Authority of Greece. The research was based onthe participation of 320 schools of secondary education from all the prefectures of Greece. Thequestionnaires used for this analysis contained data such as the annual consumption for heating andlighting, the area of the building, the number of students and professors, the installed power of theboiler, the manufacturing year of the building and the schedule of operation. Finally, the energyperformance of the school buildings in relation to the normalized annual energy consumption with floorarea and climatic severity index was rated using a fuzzy clustering technique (FCT) and an energyclassification tool has been developed.