Life Cycle Assessment is often applied as a methodological approach for evaluating the environmental performance and impact of the building sector, including building stock. In the present study, two school buildings, located in the city of Naoussa, N. Greece were analyzed, including a historic and a modern one. The survey concerned on-site inspection and documentation of the structures, data collection and analysis, Life Cycle Impact assessment, as well as comparative evaluation of the results. The objective was to indicate the constructional and performance characteristics of the buildings, as well as to comparatively evaluate their environmental performance and impact. Since historic school buildings still function as educational units, these aspects are crucial and may determine their future operation and use. For LCA, the expected life span of the buildings was taken into account (60 years for the modern school and 140 years for the historic one), as well as all life cycle stages (product, construction, use, end of life, beyond building life). Various indicators were assessed, such as Global Warming Potential (GWP), Fossil Fuel Consumption, Total Primary Energy, Non-Renewable Primary Energy. From the correlation of the results, it was asserted that although the two buildings present similar operational characteristics and needs, they have different environmental performances and impacts, mainly attributed to their different service life and structural characteristics. Although the operational GWP value of the historic building is higher (due to the extended life span), the embodied one is significantly lower (due to the natural materials used for its construction). Other indicators, such as fossil fuel consumption are also higher in the case of the modern school building, indicating that its environmental footprint is more intense.