Background: We investigated adolescents' feelings of thermal comfort during the educational process in various geographical locations far apart and present recommendations for the adjustment of the thermal environment in schools. Methods: The prospective international multicenter study took place in 8 locations on different continents. The survey in the form of a questionnaire was carried out among 2800 healthy high school students. The study was divided into "cold season survey," "warm-season survey," and heat wave survey. Results: The statistically significant difference between the "cold season survey" score of 4.04 (discomfort) and "warm-season survey" score of 3.47 (slight discomfort) (p = 0.04) indicates that students feel more thermal discomfort during winter months in all 8 locations. The heat wave survey score was 4.53 (discomfort). During the cold season, 29.24% of high school students felt themselves in full thermal comfort and 76.48% of the students felt themselves relatively comfortable (slightly cool--comfortable--slightly warm). Conclusions: Even during the ongoing process of climate change, the cold season discomfort remains the main problem for students in classes. This tendency is present in different continents as a universal problem. We recommend keeping an entrance hall and classroom temperatures at different levels and to advise students about proper clothing.