In the curriculum of lower secondary level, many important terms and phenomena of heat theory are listed (temperature, heat, amount of heat and thermal expansion, forms of heat transport, changes of state, connections between the particle structure and fundamental heat phenomena, etc.). In the description of the content, it is emphasized several times that the everyday experiences of the students should be assumed. In fact, physical processes play an important role in the functioning of common devices (e.g. refrigerator) and in the everyday life of the students: for example, the transport of heat when heating and cooking. Schoolchildren come to the physics class with diverse ideas about physical facts that they have developed on the basis of experiences and observations. Often these ideas brought with them do not agree with the scientific theories with which the learners are confronted in the classroom. The clash of different ideas is often the cause of learning difficulties. Pre-lesson ideas are also known about the phenomena of thermodynamics, for example it is common among learners that metals are cold and wood or wool are warm. In order to recognize the ideas of the learners in the classroom and to be able to take them into account for the lesson planning, a professional lesson perception is helpful. The use of video vignettes is intended to train students' perception.