Intraindividual variability is a key component in explaining children's development and learning. Studying this type of variability on the micro-timescale can help us understand real-time constructive processes and the subsequent long-term development. The aim of this article is to study the process of children's understanding of floating and sinking "during" one single-task session. A total of 38 kindergartners were asked to explain the floating or sinking of 14 different objects. The results reveal that the majority of children showed a high degree of intraindividual variability. In general, most children had a decrease in variability of both content and complexity of explanations during one task session and stabilized in both complexity and content toward the end of the task. The analyses indicated that hypothesis testing was not related to changes in children's explanations. These results can be the starting point for further research about change on different, nested timescales.