Previous research has demonstrated how young children can identify the signal in data. In this exploratory study we considered how they might also express meanings for noise when creating computational models using recent developments in software tools. We conducted extended clinical interviews with four groups of 11-year-olds and analysed the videos of the children's activity through a process of progressive focusing. In this paper we explain the design of our tasks and report how the children's expressions for noise, supported by the need to communicate with the software, developed from specific values to verbal expressions of uncertainty such as 'around', to offering ranges of values. We consider the opportunities and constraints of such an approach, which we call "purposeful computational modelling".