Airtight and highly insulated educational buildings are subjected to overheating risks, even in moderate climates, due to unforeseeable events like frequent heatwaves (HWs) and power outages (POs) leading to heat-stress and negative impact on the health conditions and cognitive performance of the students. The focus of this paper is to evaluate thermal resilience for two lecture rooms equipped with the low-energy cooling strategies natural night ventilation (NNV) and indirect evaporative cooling (IEC). To assess the thermal resilience to overheating, the lecture rooms were tested with and without passive cooling strategies for 3 Typical meteorological years (TMYs), 3 severe HWs and those 3 HWs + POs. Results evaluating the existing indicators unmet degree hours, indoor overheating degree (IOD), ambient warmness degree (AWD), and overheating escalation factor (αIOD) demonstrated that with passive cooling strategies the two test lecture rooms have good thermal resilience during TMY and HW periods (except long-term severe HW), with 18% higher unmet degree hours during HWs. Lecture room with heavier thermal mass demonstrated higher thermal resilience to overheating in long-term assessment. Furthermore the need to develop a holistic resilience indicator taking into account building and system parameters was also pointed out in this study.