This paper discusses the principles of Bioclimatic Architecture from the Post-Occupancy Evaluation (POE) with emphasis on the environmental comfort of classrooms in existing high school in the city of Passo Fundo, RS, Brazil. The Post-Occupancy Evaluation (POE) studies the built environment during its use, that is, when it becomes a lived and felt space. Data related to environmental comfort and user perception were collected in six classrooms during the daytime (morning and afternoon). To evaluate the perception of the users within the classrooms, questionnaires were applied to students and teachers, with topics on satisfaction with the environment, thermal sensations, and suggestions for improvement in school. The results confirmed the need for readjustment of the classrooms, mainly due to the typology and arrangement of the external openings (windows), since the noise indexes exceeded the acceptable and normative values for a comfortable use of the school environment.