To be able to cope with complex systems, it is important for mathematics education that children have experience with situations in which they gradually engage the real problem with complex systems and interdisciplinary complex systems at starting from the primary school. In doing this, mathematical modeling consisting of cycles of model eliciting and relating model with real-life is one of the available approaches. Therefore, the purpose of this study was to reveal the models of fourth-grade primary-school children, who have no prior experience with modeling problems in their classroom. This research study was conducted during the 2016-2017 academic year, in a university-foundation primary school in a large city along the Black Sea Region of Turkey. Participants were a total of 20 children in one of the 4th grades. The children in groups of four were assigned a modeling activity, the Hairdresser Salon Problem, to work on for two class-hours as a group. Modeling processes of each group and presentations at the end were video and audio-taped. The mathematical thoughts, developed models, written responses of the primary-school children were qualitatively analyzed in the light of the modeling cycle developed by Blum and Fern . The results showed that children were able to concert symbolic data into numerical data, take into account of different parameters (hair cutting and washing cost, waiting time, distance from home, hair washing time, hair cutting time, hair styling time and customer satisfaction) together and make mathematical calculations in the modeling process. At the end, they presented and explained their models if they were appropriate.