Nineteen university students were asked about their thermal comfort while attending ordinary lessons in a displacement ventilated test room of typical classroom size. Two different ceiling heights were tested. Both the general temperature level and the strength of the vertical temperature stratification in the room increased continuously during the lessons due to the presence of the students, however slower with the higher ceiling. The temperature stratification of the air eventually reached a strength of 3.1°C/m, which, according to international standards, should cause some complaints about the thermal comfort. There was however no indication of that the students could feel this stratification. The fact that the vertical radiative temperature asymmetry was comparatively small in the room – due to radiative heat exchange between the interior surfaces – is believed to be a major reason for this insensitivity of the students to the vertical air temperature stratification.