This paper presents the first results of a field study on thermal comfort in school buildings that is been carried out in Chile, with the aim of determining comfort temperature of students in state-owned primary schools. The paper presents the results of four schools located in Santiago, a city with low temperatures in winter and high temperatures in summer, which are typically free-running, as they have neither a heating nor a cooling system. The methodology included measurements of thermal parameters complemented with questionnaires based on the adaptive model and modified for the understanding of 9-10 years-old students. The field work was organized in two phases: winter (August) and summer (December), where in each phase the students responded the questionnaire up to three times per day in a period of three to four days. The results show that comfort temperature derived from the field work is significantly lower than comfort temperature calculated from Humphreys formula, while they also show that students form highly vulnerable schools voted lower comfort temperatures than those from less vulnerable realities.