Öz
Within the scope of the research, three different geometric modeling problem activities were carried out during a three-week period in a geometry-teaching course at a state university. As part of this comprehensive study, the modeling competencies of pre-service mathematics teachers in the "Is the base or half the height?" geometry problem were examined. The participants of the study were thirty-seven fourth grade students of middle school mathematics education and they were selected according to the purposeful sampling method. The data of the study were collected through worksheets and concrete geometric models designed by pre-service mathematics teachers. The participants were given a geometry problem case that included the proof of the triangle’s area formula, and the pre-service teachers were asked to make the mathematical solution and then design and present it in the form of geometric concrete models. The data were analyzed through the rubric developed in terms of the mathematical understanding, the processes of transforming geometric shapes and the geometric model they designed. Findings showed that most of the pre-service teachers solved the geometric modeling problem correctly and created functional models. In addition, while creating concrete geometrical models, the pre-service teachers took into account their previous mathematical knowledge and put their spatial skills to work.