This study investigates the nature and role of common ground in group learning of mathematics by means of the analytical construct of focal projects and contextualization. The analysis investigates two students (12-13 years old) playing a dice game, where they are to distribute a set of markers based on the totals of two dice. The analysis shows how the consistency between the students’ focal projects became critical to their progression from a uniform to a non-uniform distribution of the markers. The task system and concrete manipulatives became crucial in furthering the students’ explorations. In the frame of a frequency context, we also discuss how a contextualization may restrict certain aspects of probability from coming into play during such explorations.