Climate change (CC) and urban heat island (UHI) are important environmental forces that have serious consequences for the existing buildings, such as increased resource consumption and environmental footprint, adverse human health effects and reduced occupant comfort. In this context, educational buildings represent a critical category amongst other building typologies, due to their high energy use, high occupant density, atypical daily/annual occupancy patterns, and their occupants' high vulnerability to heat. Poor indoor conditions can reduce the health and productivity of students and teachers, worsen learning performance and reduce attendance. Retrofitting educational buildings is an effective solution to tackle this challenge. This study investigates the impact of CC&UHI on educational building performance and demonstrates the effectiveness of passive retrofit scenarios targeting CC&UHI mitigation and adaptation. These investigations are based on a systematic approach that consists of (i) the generation and analyses of CC&UHI-modified weather datasets, and (ii) simulation-based comparative analyses of the as-is building and various retrofit scenarios. An existing secondary school building in Ankara, Turkey is selected as a case study for evaluations of the selected performance indicators including energy use, global warming potential (GWP) and thermal comfort. Obtained results indicate that total energy consumption can be reduced up to 50% with retrofit, whereas possible reductions in indoor discomfort are even more pronounced, underlining the significance of selecting the optimal combination of passive measures for maximum impact towards the adaptation of the existing educational buildings to the changes in climatic conditions.