This study aims at investigating the relationship between deterministic and probabilistic reasoning when students are asked to model and predict the outcomes of a real-world situation involving uncertainty. Twelve students, aged 8-9 years, participated in an outdoor located teaching activity which called for reflection on the growing of sunflowers. Based on the analysis, and previous research, the study suggests to structure an analysis on the relationship between deterministic and probabilistic reasoning according to four analytical relationships: Deterministic model and deterministic behaviour; Deterministic model and probabilistic behaviour; Probabilistic model and deterministic behaviour; Probabilistic model and probabilistic behaviour.