In this study, it was aimed to investigate 4-to-6-year-old children's reasoning skills appearing in pattern tasks. 55 children studying in the classes of four different pre-school classes participated in the study. A classroom teaching experiment was conducted to examine the development of children's reasoning skills in pattern tasks. Both qualitative data and quantitative data were collected. Qualitative data consists of video and audio recordings of children's pattern tasks and pattern worksheets. Quantitative data includes the database of scoring children's pattern studies according to the pattern structure scheme proposed by Clements and Sarama (2009). The reasoning levels of children in pattern tasks were analyzed using the Winsteps Rasch software. In the pattern tasks included in the study, the reasoning skills of children were addressed with Wright Map and were supported by direct quotations from children's pattern activities. It was observed that children could do copying and expansion activities easily in pattern tasks. In abstraction tasks, reasoning skills with a high cognitive level were effective. Based on the study results, it has been concluded that younger children's reasoning skills are effective and can be developed when they are exposed to pattern tasks.