The mean of the reasoning strategy in experiment and control groups are 2,65 and 1,73 in sequence. The t–test was used to determine whether the difference is significant or not, and calculated 2,17 t-value is found significant in 0,05 level. Many problem solving strategies contain reasoning, so activities in experimental applications were aimed to develop reasoning. As a result of this aim, it was seen that students had the ability to think systematically at the end of the application