This study investigates the relationship between deterministic and probabilistic reasoning when students are asked to experiment on a real-world situation involving uncertainty. Twelve students, aged eight to nine years, participated in an outdoor teaching activity that called for reflection on the growth of sunflowers within the frame of a sunflower lottery. A basic feature of the situation was that the students were involved in the process of creating their own empirical data of the growth. However, the study shows not only that the students do not make use of data for predicting the outcome of an uncertain event, but also how this can be explained by students' attention to deterministic features of the situation, brought to the fore within an ecology context and connected to a conceptual principle of ‘sharing’.