Today’s society is becoming increasingly complex. To effectively function and develop in this society, all citizens need to overcome misconceptions about probability, and foster an ability of probabilistic reasoning instead. According to previous research, both theory and experiment are essential for the development of such reasoning. Japanese high school probability lessons, however, do not place great importance on the link between theory and experiment. Consequently, the more Japanese high school students study probability, the more they fail to accept probabilistic reasoning. To address the aforementioned issue, this paper aims to develop a high school probability lesson that will encourage development of the ability of probabilistic reasoning. The teaching material used will be the problem of “Effect of sample size”. To answer the research question, students need to think probabilistically and use the concept of repeated trials, which is a part of the high school probability curriculum. For the interplay between theory and experiment, we used TinkerPlots Software to visualize the process of data generation. As a result, we developed a lesson and showed that it is effective for the development of the ability of probabilistic reasoning.