This paper describes students' developing meta-representational competence, drawn from the second phase of a longitudinal study, "Transforming Children's Mathematical and Scientific Development." A group of 21 highly able Grade 1 students was engaged in mathematics/science investigations as part of a data modelling program. A pedagogical approach focused on students' interpretation of categorical and continuous data was implemented through researcher-directed weekly sessions over a 2-year period. Finegrained analysis of the developmental features and explanations of their graphs showed that explicit pedagogical attention to conceptual differences between categorical and continuous data was critical to development of inferential reasoning.