This paper reports findings from a classroom based study with 5 year old children in their first term of school. A data modelling activity contextualised by a picture story book was used to present a prediction problem. A data table with numerical data values provided for three consecutive days of rubbish collection was provided, with a fourth day left blank. Children were asked to predict the amount of rubbish collected on the fourth day and to explain their prediction. The results revealed children's intuitive probabilistic reasoning competencies and the influence of task design on their reasoning.