Although natural ventilation can greatly affect indoor heat and energy use, little is known about how opening windows for natural ventilation affects indoor thermal conditions, especially in hot dry climates. During the pre-design phase of a school building, it is critical to consider the environmental response to the design of the interior space. This paper examines the impact of utilizing natural ventilation through windows on the temperature regulation of classrooms within a school located in a hot and arid climate. Temperature data loggers were installed in four classrooms that were oriented in the main directions. After that, a calibration was made between the real data and simulation data. All four classes took part in the simulation process throughout the year and the windows were opened and closed. Due to the hot climate in the Qassim region, the windows are only opened during study periods when the indoor temperature is higher than the outdoor temperature. Field data results show that creating a friendly environment inside a building is influenced by factors including wall exposure, window size and orientation. Regarding the simulation, the temperature effect can be significantly affected by natural ventilation in the four classes. Results indicate that from late November until early April, the indoor temperature was still below the upper limit of acceptable indoor temperatures recommended by ASHRAE, 27°C, and thus, achieved 20% occupancy dissatisfaction. In contrast, from April until late November, the indoor temperature increased.