Making toddlers' numerical competence visible - without relying solely on verbal utterances

There is a growing consensus in research that children's numerical competence starts to develop at a very early age. However, there are few tools for screening the development of early numerical competence and thereby making this development researchable. One obstacle in designing such tools is that verbal utterances cannot be used as the primary source for exploring the numerical competence of young children. The focus of this article is methodological, namely how toddlers' (1-3-year-olds') ways of experiencing numbers can be made visible in research without relying solely on verbal utterances. A theoretically driven interview tool was developed based on five principles of: context, numbers, process, multiple-method activity approach, and differentiation. The two principles of numbers and process vouched for internal validity, while the three principles of context, multiple-method activity approach and differentiation vouched for external and ecological validity. Examples of empirically tested interview tasks are also presented and discussed.