The purpose of this study is to introduce a problem-based learning (PBL) scenario that elementary school science teachers in middle school (5th-8th grades) can use in their in-service training. The scenario treats the subjects of heat, temperature and thermal expansion within the scope of the 5th and 6th grade science course syllabi and has been drawn up to represent the stage-by-stage solution of a real life problem. The scenario was tried out in 2014 as a research project funded by the Scientific and Technological Research Council of Turkey (TÜBITAK) in different geographical regions and provinces of Turkey (7 regions and 26 provinces) with 40 elementary school science teachers (20 women and 20 men). The face-to-face interviews conducted with 11 participating teachers and the unstructured observations made throughout the PBL scenario that is introduced in this article reveal that such a scenario is effective and useful and can be used during in-service teacher training.