The research analyzes the performance of a simple rule-based control to perform demand response (DR) using the building thermal mass (BTM) in non-residential buildings. The DR schedule-based controller is implemented and tested for two months in a highly-insulated school located in Trondheim (Norway). Simple DR control can be considered as an intermediate step before implementing more advanced controls, such as model predictive control (MPC). In addition, there is a lack of knowledge and field experiments on thermal comfort during transient indoor thermal environments, especially in educational buildings. Firstly, the experiments show that a simple schedule-based controller in a recent building can still experience basic faults during operation. Secondly, the simple DR control decreases the delivered space-heating energy by 27% during peak hours for a moderate increase of delivered energy of 18%. Thirdly, while the thermal sensation is altered during DR, the thermal satisfaction remains high. The indoor temperature decay during DR is below the recommended thresholds given by the ASHRAE 55–2017 standard. In conclusion, the study bridges the gap between simulation-based studies and real-world applications. Results demonstrate the ability of a simple DR control to perform load shifting with a moderate but significant increase in energy use and without jeopardizing the thermal comfort of the occupants.