This paper tracks the individual development of metacognition in two five year old children over an academic year as they engage in a cognitive acceleration through science education programme CASE@KS1. Using qualitative analysis and case study methods it demonstrates how collaborative group work with small children impacts on the development of their individual metacognitive processing. Important variables that facilitate or hinder this development are teased out and relationships between the groups and the individual are analysed. Difficulties with the concept of metacognition and in particular how to assess and measure it are discussed. A framework of analysis based on verbal interactions is developed from the early theories of metacognition and this is combined with an in-depth grounded analysis. This approach provides insight into what we can mean when we speak of young children being metacognitive.