There has been various researchers' focus on "heat transfer". "Convection, radiation and conduction" discussed as mere elements of the wider object of analysis in these research. Given the lack of sufficient emphasis on conduction in solids, no cross-age research conducted with pre-service science teachers supported by drawings, interviews, and open-ended questions could be found. Employing a cross-age design, this research determined pre-service science teachers' (PSTs') conceptions in the "conduction of heat in solid". The sample group of the research consists of 257 PSTs (first year student--n=55; second year student--n=76, third year student--n=56, and fourth year student--n=70) selected from Department of Science Education in Fatih Faculty of Education at the Karadeniz Technical University in the city of Trabzon in Turkey. Conceptual understanding test and semi-structured interview were used in the data collection process. The test including two questions was administered to 257 PSTs from different years. Semi-structured interview including one question was conducted with 16 voluntary PSTs (4 students from each grade level). The research found that PSTs had difficulties in terms of describing and showing the movement of the particles of solid under the impact of heat. In the light of the findings, it can be suggested that animations should be used to the teaching of the movement of the particles under the impact of heat.